Research & Publications

Organoid Pharmacotyping of Pancreatic Cancer Enables Functional Precision Oncology and Drug Repurposing

Nicholad R. Jette, MD, PhD, Franco Vizeacoumar, PhD, He Dong, MSc, Frederick S. Vizeacoumar, PhD, Yue Zhang, PhD, Jared D.W. Price, BSc, Vincent Maranda, BSc, Lihui Gong, BSc, Tanya Freywald, MSc, Patrick Vizeacoumar, BSc, Rani Kanthan, MD, Yuliang Wu, PhD, Kathleen Felton, MD, MSc, Bilal Marwa, MB-BS, Laura Hopkins, MD, Gar Groot, MD, PhD, John Shaw, MBBCh, MMed(surg), Mike Moser, MD, MSc, Andrew Freywald, PhD, Shahid Ahmed, MD, PhD, Adnan Zaidi, MD

University of Saskatchewan

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy, characterized by chemoresistance and insufficient genomic predictive models for therapy response. This study aims to explore patient-derived organoids (PDOs) as a platform for functional precision oncology and systematically pharmacotype genomically annotated PDAC PDOs.

Methods: A clinically annotated panel of ten treatment-naïve PDAC PDOs, encompassing well-, moderately-, and poorly differentiated tumors, was established. The PDOs were assessed for morphological and genomic fidelity and screened against 1,813 agents using a high-throughput system. Drug sensitivities were evaluated at both the compound and drug-family levels and correlated with histological grade, mutational profiles, and available clinical treatment data.

Results: PDOs preserved key tumor features, revealing both shared and subtype-specific vulnerabilities. Well and moderately differentiated PDOs showed enriched mutations in DNA repair and chromatin-regulatory pathways, displaying sensitivity to topoisomerase inhibitors and HDAC inhibitors. Conversely, poorly differentiated PDOs exhibited coordinated defects in mitochondrial function that led to a novel vulnerability to cardiac glycosides. Sensitivities to standard PDAC therapies varied significantly across models, highlighting the limited predictive power of genotyping alone.

Conclusion: This multi-faceted genomic and pharmacologic analysis confirms that PDO pharmacotyping uncovers biologically relevant vulnerabilities in PDAC, presenting new therapeutic avenues, particularly for basal, chemo-resistant tumors. PDO-guided functional profiling is thus essential for refining drug selection and expanding treatment options for PDAC patients.

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The evolving landscape of axillary lymph node dissection in breast cancer: A population-based study

Matthew Castelo, MD, PhD 1, FRCSC, Tulin D. Cil, MD, Med, FRCSC 1, Amanda Roberts, MD, MSc, FRCSC 1,  Gary Ko, MD, FRCSC 1, Lena Nguyen, MSc 2, Wanda Marini, MD PhD, FRCSC 1, Jenine Ramruthan 3, Emma Reel MSW 3

1 University of Toronto, 2 ICES, 3 University Health Network

Introduction: Indications for axillary lymph node dissection (ALND) in breast cancer (BC) have declined, and the procedure is now largely reserved for complex cases. We examined temporal trends in ALND and described surgeon-level procedural volume.

Methods: We conducted a population-based cohort study using linked ICES administrative datasets in Ontario, Canada. Adults (≥18 years) with non-metastatic BC diagnosed between April 1, 2012, and December 31, 2024, were identified in the Ontario Cancer Registry and linked to OHIP billing data. ALNDs and the performing surgeon were identified using OHIP billing codes.

Results: After exclusions, 126,343 women underwent surgery for Stage I-III BC between 2013-2024 in Ontario. The proportion receiving ALND declined from 29% in 2013 to 12% in 2024. Post-pandemic, ALNDs increased among patients undergoing upfront surgery, while ALNDs after neoadjuvant chemotherapy fell sharply. From 2022-2024, half of all ALNDs occurred in upfront surgery patients, and only 37% had a preceding SLNB. Among surgeons performing ALND, median annual volume decreased from 4 in 2013 to 2 in 2024, and early-career exposure declined from 2.5 ALNDs in the first two years of practice (2013-2014) to 1 (2019-2020).

Conclusion: ALND is now infrequently performed, with growing concentration among low-volume, late-career surgeons. ALNDs after neoadjuvant chemotherapy have been decreasing rapidly since 2020, likely reflecting greater uptake of SLNB after neoadjuvant chemotherapy and increasing rates of complete pathologic response. Declining ALND exposure for new surgeons highlights the need to assess training implications and whether procedural volume influences outcomes in BC patients.

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Chronicled Experiences of Breast Cancer: Analysing Adjuvant Endocrine Therapy on TikTok

Nina Morena, MA 1, Ari N. Meguerditchian, MD, MSc 2, Jillian Schneidman 1, Victoria Hayman 1, Tanya Odisho 1, Marya Alsuhaibani 1, Simon Rahman 1, Suzanne Simba 1, Eric Belzile 2

1 McGill University, 2 St Mary's Research Centre

Introduction: Women with breast cancer (WBC) face particular challenges related to adherence to adjuvant endocrine therapy (AET). The aim of this study is to evaluate how WBC describe their experiences with AET on TikTok.

Methods: Videos tagged with #tamoxifen and a range of related terms on TikTok were collected in 08/25. Video characteristics collected included: username, user profile, caption, length, date posted, number of followers, likes, views, shares, and comments, and creator demographics if available. Sentiments regarding AET-related experiences and potential discontinuation were collected. The Kruskal-Wallis test was performed to test the association between variables.

Results: 167 English language videos were included. Average video length was 2.3 minutes (SD 2.2). 24 used music; 10 used audio memes. Mean follower number was 20,170 (SD 68,260). Mean number of views, likes, and comments was 9,048 (SD 16,322), 194 (SD 279), 52 (SD 84), respectively. The majority were filmed at home (71%), 19% in the car. Most common age range was 30-39 years old (54%), followed by 40-49 (27%). In 87%, the creator had already initiated AET. 15

Conclusion: TikToks on AET by WBC describe the daily experience of managing side effects, including potential discontinuation reasons, and offer insights into patient perspectives. Online communities related to general unwellness are emerging on TikTok.

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Trends in breast recons1truction for BRCA1/2, PALB2 and other high penetrance germline pathogenic variant carriers undergoing risk reducing mastectomy

Amel Melanson, MD(c) 1, Marya Alsuhaibani, MD 1, Alex Viezel-Mathieu, MD MSc 2, Tassos Dionisopoulos, MD 2, Mark Basik, MD 1, Jean-Francois Boileau, MD MSc 1, Karyne Martel, MD 1, Ipshita Prakash, MD MSc 1, Sarkis Meterissian, MD MSc 1, Joshua Vorstenbosch, MD PhD 2, Stephanie M. Wong, MD MPH 3

1 Department of Surgery, McGill University, 2 Department of Plastic and Reconstructive Surgery, McGill University, 3 McGill University

Introduction: Women with germline pathogenic variants (GPVs) in BRCA1/2, PALB2, or other high-penetrance genes may consider risk-reducing mastectomy (RRM), with or without reconstruction, to reduce their risk of developing breast cancer. Few studies have characterized reconstructive trends within this patient population.

Methods: We conducted a retrospective cohort study of female patients with a confirmed GPV in a high-penetrance breast cancer susceptibility gene who underwent RRM between 2003 and 2024. Clinicodemographic and surgical data were extracted from electronic medical records. The Chi-squared test and Mantel-Haenszel test for trend were used to evaluate factors and temporal trends associated with reconstruction.

Results: Of 443 female GPV carriers who underwent RRM, 394 (88.9%) elected to undergo breast reconstruction. Factors significantly associated with reconstruction included younger age (p < 0.001), premenopausal status (p < 0.001), and more recent year of RRM (p = 0.04). Among women undergoing reconstruction, the median age was 43 years (IQR 35–52), compared to 55 years (IQR 39–65) in those electing no reconstruction (p < 0.001). There was a significant trend toward increased use of reconstruction over the study period (85.2% prior to 2012 vs. 97.0

Conclusion: In BRCA1/2, PALB2, and other high-penetrance GPV carriers undergoing RRM, the use of reconstruction increased from 85% prior to 2012 to 97% in 2022. Implant-based techniques were the most commonly used, although autologous/flap-based reconstruction methods gradually increased over time. Further research examining patient-reported outcomes, recovery time, and the financial impact of different reconstructive approaches is warranted.

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Intravenous Albumin in Surgical Oncology Patients: A Systematic Review and Meta-Analysis

Aviva Moses, BHSc 1, Jeannie Callum, MD 2, Oladele Situ, MBBS 3, Bram Rochwerg, MD, MSc 4, Wiley Chung, MD, MHPE 5, Albumin Systematic Review Research Team 6

1 Faculty of Health Sciences, Queen’s University, 2 Department of Pathology and Molecular Medicine, Queen’s University, 3 Division of General Surgery, Department of Surgery, Temerty Faculty of Medicine, University of Toronto, Breast Surgical Oncology Fellowship Program, University of Toronto, 4 Department of Medicine and Department of Health Research Methods, Evidence & Impact, McMaster University, 5 Department of Surgery, Queen's University, 6 Various Affiliations.

Introduction: Intravenous albumin is commonly administered during surgical oncology procedures despite limited evidence of benefit. This systematic review and meta-analysis evaluated whether albumin administration, compared to alternative fluid strategies, improves outcomes in patients undergoing cancer surgery.

Methods: We searched MEDLINE, EMBASE, and Cochrane databases from inception to March 5, 2025, without language restrictions, following PRISMA and Cochrane guidelines. We included randomized controlled trials (RCTs) comparing albumin with alternative fluid strategies (crystalloids, synthetic colloids, or no albumin) in adult cancer surgery patients. We evaluated outcomes rated as important or critical by an expert panel, performed meta-analyses using random-effects models, and assessed certainty of evidence using GRADE.

Results: We included nine RCTs (n=890 patients), five of which used crystalloids as the comparator. Pooled analysis found there may be no difference between albumin and alternative fluid groups in total complication rates (risk ratio [RR] = 0.96; 95% confidence interval [CI]: 0.68 to 1.35), intensive care unit or hospital length of stay, or perioperative blood loss (all low to moderate certainty). Effects on mortality and inotrope/vasopressor use were uncertain (very low certainty). Albumin administration was probably associated with a lower perioperative fluid balance (mean difference [MD] = -169.97 mL; 95% CI: -293.41 to -46.52, moderate certainty).

Conclusion: Current evidence suggests albumin may not improve patient-important outcomes in surgical oncology. The modest reduction in fluid balance observed with albumin is unlikely to be clinically meaningful, and routine albumin use may contribute to unnecessary healthcare costs. Larger, multicentre RCTs are needed to guide evidence-based perioperative fluid management in surgical oncology.

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Prognostic Impact of Anatomic Subsite in Head and Neck Cutaneous Melanoma: A 50-Year Population-Based Study

Uriel Clemente-Gutierrez, MD 1, Alok Pathak, MBBS, MS, PhD, MHM 2, Anouska Agarwal, MSc 2, Kristin Buchko, MD 2, Mahmoud Seif-Elnasr, MD 2, Suhail Sayed, MBBS, MS 2

1 Department of Surgery, London Health Sciences Centre, Western University, 2 Head and Neck Surgical Oncology, Cancer Care Manitoba; Department of Surgery, University of Manitoba,

Introduction: "Previous studies have shown that scalp melanoma carries a worse prognosis than other head and neck subsites. However, most series combined face and neck primaries, lacked long-term follow-up, or did not adjust for surgical and histologic factors. We evaluated the independent prognostic role of anatomic subsite in a population-based cohort."

Methods: A retrospective review of 716 patients with HNCM treated in Manitoba (1970–2020) was conducted. Primary sites were categorized as scalp (n=99), face (n=479), or neck (n=138). Outcomes assessed included disease-specific survival (DSS), disease-free survival (DFS), and local recurrence-free survival (LRFS). Multivariable Cox proportional hazards models adjusted for age, sex, stage, histology, margin status, and adjuvant therapy.

Results: Median follow-up was 92 months (IQR 48–183). Scalp melanomas presented with more advanced disease: only 46.5% were Stage I, compared to 66% of face and 66.7% of neck primaries (p=0.008). Stage II–III disease was present in 53.5% of scalp cases, versus 34% of face and 33.3% of neck cases. On multivariable analysis, scalp location independently predicted worse outcomes. Compared with scalp, patients with face primaries had superior survival: DSS (HR 0.59, 95% CI 0.36–0.95, p=0.031), DFS (HR 0.47, 95% CI 0.32–0.69, p

Conclusion: Although the adverse prognosis of scalp melanoma has been reported, our population-based analysis with long follow-up confirms its independent impact across DSS, DFS, and LRFS, even after full adjustment. These findings reinforce the relevance of anatomic subsite in risk stratification and highlight the need for tailored surveillance and treatment in scalp melanoma.

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Durable local control following salvage interstitial brachytherapy for anorectal cancer pelvic recurrence: a retrospective cohort

Paul Savage MD, PhD 1, Amandeep S. Taggar MD, MSc 1, 2; Ruben Del Castillo Pacora MD 1, 2; John M. Hudson MD, PhD 1, 2; Michael J. Raphael MD, MSc 1; Shady Ashamalla MD, MSc 1

1 Department of Surgery, University of Toronto; Odette Cancer Centre Sunnybrook Health Sciences Centre, 2 Department of Radiation Oncology, University of Toronto,

Introduction: Salvage surgery is the standard-of-care for patients with pelvic recurrences from anorectal cancers, including rectal adenocarcinoma and anal squamous cell carcinoma (ASCC). Given the associated morbidity, some patients decline surgery, while others are considered unresectable, and controlling pelvic disease in these patients remains a major challenge. Interstitial brachytherapy (ISBT) has demonstrated efficacy in early-stage anorectal malignancies, yet its role in the recurrent setting is undefined.

Methods: A retrospective analysis on a cohort of consecutive patients with anorectal cancer pelvic recurrences treated with ISBT between January 2018 and February 2025 at a single Canadian tertiary center was performed. Cumulative incidence function was used to estimate in-field local, out-of-field pelvic and distant progression and Kaplan-Meier was used to estimate overall survival.

Results: Fourteen patients (10 adenocarcinoma and 4 ASCC) were included, with a median target lesion size of 3.7 cm. Six (42.9%) patients were treated with EBRT and ISBT (median 17.3 Gy), while 8 (57.1%) received ISBT alone (median 30 Gy). The overall response rate was 57.1% and median duration of in-field target control was 22.1 months. Median overall survival was 31 months. Out-of-field pelvic and/or distant progression were the predominant patterns of failure, with only one (7.1%) patient demonstrating isolated in-field progression and 3 (21.4%) patients dying with isolated pelvic disease. Grade 3 toxicity, including fibrotic and necrotic complications, was observed in 6 (42.9%) patients.

Conclusion: Salvage ISBT results in durable control for anorectal cancer pelvic recurrences with favorable toxicity profile. Distant relapse often precedes local progression in this high-risk population and death from isolated uncontrolled pelvic disease is rare using this strategy.

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Impact of decision regret on psychosocial outcomes after surgery in women with unilateral breast cancer.

Oladele Situ, MBBS 1, 2; David W. Lim, MDCM, MEd, PhD 1, 3, 4, 5, 6; Aghaghia Mokhber, HBSc, 3,7; Katelynn Tang, MD, 1, 8; Anne C. O'Neill, MBBCh, MMedSci, MSc, PhD 9, 10; Tulin D. Cil, MD, MEd, 1, 11, 12; Toni Zhong, MD, MHS 9 10; Stefan O. P. Hofer, MD, PhD, 9, 10; David R. McCready, MD, MSc 1, 11; Kelly Metcalfe, RN, PhD 3, 13

1 Division of General Surgery, Department of Surgery, Temerty Faculty of Medicine, University of Toronto, 2 Breast Surgical Oncology Fellowship Program, University of Toronto, 3 Women’s College Research and Innovation Institute, Women’s College Hospital, 4 Institute of Medical Science, Temerty Faculty of Medicine, University of Toronto, 5 Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, 6 Department of Surgery, Women's College Hospital, 7 Queen’s School of Medicine, Queen’s University, 8 Division of General Surgery, Department of Surgery, North York General Hospital, 9 Division of Plastic Surgery, Sprott Department of Surgery, University Health Network, 10 Division of Plastic, Reconstructive & Aesthetic Surgery, Department of Surgery, Temerty, 11Division of General Surgery, Sprott Department of Surgery, University Health Network, 12 Institute of Medical Science, Temerty Faculty of Medicine, University of Toronto, 13 Lawrence S. Bloomberg Faculty of Nursing, University of Toronto

Introduction: We aim to determine whether decision regret after surgery affects psychological outcomes in women who choose mastectomy over lumpectomy for stage 0-III non-hereditary breast cancer.

Methods: A prospective cohort study at the University Health Network involving women with unilateral non-hereditary cancer was conducted (2014 – 2017). Surgery type [unilateral lumpectomy (UL), unilateral mastectomy (UM), and bilateral mastectomy (BM)] was recorded. UM indications were categorised as oncological (UMO) or patient’s choice (UMC). Decision Regret Scale (DRS), BREAST-Q, Impact of Event Scale, and Hospital Anxiety and Depression Scales were completed at 12 or 18 months post-surgery. Univariable and multivariable linear regression models were adjusted for demographic, clinical, and treatment factors; significance was set at P

Results: Of 217 women studied, 51 had UL, 71 had BM, and 95 had UM. Twenty-four had UMC. UM had significantly higher DRS scores than UL (8.3 vs 17.4; P < 0.01), and this persisted in the UMC subgroup after covariate adjustment (β = 16.0, SE = 7.6, P=0.04). Higher DRS in UMC was related to lower breast satisfaction (β = -1.0, SE=0.5, P=0.03) and psychosocial well-being (β = -0.8, SE=0.4, P=0.02). Depression scores were higher in UMC compared to UMO (4.9 vs 2.8; P 

Conclusion: Women with unilateral, sporadic breast cancer who chose unilateral mastectomy experienced higher decision regret and lower satisfaction and psychological well-being after surgery than those who chose lumpectomy or bilateral mastectomy, irrespective of reconstruction.

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Rates of pathologic complete response in patients with stage I triple negative breast cancer treated with neoadjuvant chemotherapy: an updated analysis

Pamela Brazeau-Porrello, MD 1, Jena Bertagnolli 2, Sofia Tiseo 2, Stephanie M. Wong, MD 3, 4; Mark Basik 1, Jean-François Boileau 1, Karyne Martel 1, Sarkis Meterissian 1, Ikhtiyar Al Tubi 1, Ipshita Prakash 1

1 Department of Surgery, McGill University, 2 McGill University Medical School, 3 Division of Plastic Surgery, Sprott Department of Surgery, University Health Network, 4 Division of Plastic, Reconstructive & Aesthetic Surgery, Department of Surgery, Temerty Department of Surgery, McGill University

Introduction: The use of neoadjuvant chemotherapy (NAC) in stage I triple negative breast cancer (TNBC) is controversial. Clarifying the efficacy of NAC in this sub-group is critical to guide clinical decision-making. Our study seeks to evaluate the pathologic complete response (pCR) rate and potential predictors of the response to NAC in this under-studied population.

Methods: Stage I TNBC patients (cT1N0) treated with NAC between 2005 and 2025 were identified. Patient clinical characteristics were compared via Chi-square or Fisher's exact tests. Multivariate logistic regression was performed to identify factors associated with pCR.

Results: Of n=351 stage I TNBC patients, n=104 (29.6%) were treated with NAC. Of those, n=12 (11.5%) had cT1a–b tumors and n=92 (88.5%) had cT1c tumors. The median age was 55 years (IQR 43.8-64.0 years). Twenty-seven patients (26%) had grade 1-2 tumors, while n=77 (74%) had grade 3 TNBC. NAC regimens included anthracycline-containing in 84.6% and anthracycline-free in 14.4%. Overall, the pCR rate was 58.7%. In multivariate logistic regression analysis, grade 3 tumors (aOR 2.80, 95% CI 1.06-7.74) and age

Conclusion: Our findings suggest that the pCR rate of stage I TNBC patients treated with NAC is similar to that previously reported for stage II-III patients. Larger studies with longer follow-up are needed to evaluate the prognostic implications of pCR in this population.

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Presentation and management of perforated rectal cancers associated with abscess or fistula: a retrospective case series

Susie Youn, MD, Jason Park, Abdullah Mashat

University of British Columbia

Introduction: Perforated rectal cancers associated with peri-tumoral abscess or fistula are a rare presentation with unique clinical considerations, including their ability to tolerate neoadjuvant therapy and obtain negative margins at the time of surgery. Their prognosis compared to other locally advanced rectal cancers is unknown. This retrospective case series aimed to describe the presentation, management, and survival outcomes of a set of patients with perforated rectal cancers.

Methods: Chart reviews were performed of T4 rectal adenocarcinomas in a prospectively collected database in British Columbia, Canada from 2017-2021 to identify tumors associated with pelvic or perianal abscesses and/or fistulae. Staging MRI scans were reviewed to identify the nature of each perforation. Data on patient demographics, tumor characteristics, surgery, neoadjuvant and adjuvant treatment were collected. In patients treated with curative intent, recurrence-free and overall survival were calculated from the date of surgery.

Results: Of 204 T4 rectal cancers from 2017-2021, 32 (15.7%) patients with perforated rectal cancer were identified. Twenty-four (72.7%) patients were male, and the median age was 62 years (IQR 50-70). Four (12.5%) patients presented with synchronous metastatic disease and an additional four patients were deemed non-operative candidates due to comorbidities. Twenty-four patients (75%) were treated with curative intent, with 21 patients receiving neoadjuvant therapy (81.0% with long course chemoradiation and 19.0% with a total neoadjuvant therapy approach). Six (18.8%) patients underwent diverting ostomy prior to neoadjuvant therapy. In patients who underwent oncologic resection, 50% underwent multi-visceral resection and an R0 margin was obtained in 83.3%. Amongst patients treated with curative intent, median RFS was not reached, with 3-year RFS of 66.7% and 3-year OS of 87.5%. In comparison, patients with non-perforated T4 tumors had a 3-year RFS of 48.2% and 3-year OS of 75%.

Conclusion: To our knowledge, this is the largest case series to date describing the management and outcomes of perforated T4 rectal cancers. In this series, the majority of patients treated with curative intent received neoadjuvant therapy and obtained an R0 margin at the time of surgery. These data suggest that perforated rectal cancers, provided that acute symptoms related to abscess or fistula are managed, can safely receive neoadjuvant therapy and achieve similar oncologic results to other non-metastatic T4 rectal cancers.

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Targeted Hyperthermia Induces Immunogenic Tumor Remodeling and Demonstrates Early Clinical Response in Immunotherapy-Refractory Metastatic Melanoma

Carman Giacomantonio, MD, MSc, Barry Kennedy, PhD, Kate Clark, Cheryl Dean, Nicholas P. Cheverie, MSc, Kelly J. Corscadden, Caitlin Gormley, Geetha Subramanian, Julie L. Jordan, Erin B. Noftall

Dalhousie University

Introduction: Targeted Hyperthermia Therapy (THT) delivers controlled intratumoral heating using gold nanorods that convert near-infrared (NIR) light into localized thermal energy. This minimally invasive approach induces immunogenic cell death (ICD) and remodels the tumor microenvironment (TME), promoting immune activation in otherwise poorly inflamed tumors. Preclinical studies have demonstrated that THT can convert immunologically “cold” tumors into inflamed lesions; however, the biological processes underlying this transition, and their implications for rational combination strategies, remain incompletely defined. Here, we present mechanistic preclinical studies defining the immunogenic effects of controlled hyperthermia, together with an early clinical evaluation of THT in patients with advanced melanoma.

Methods: In a first-in-human, open-label, early feasibility study (NCT06894407), ten patients with stage 3C/3D/4M1 cutaneous metastatic melanoma progressing on immune checkpoint inhibitors received intratumoral gold nanorods (Sona Nanotech Inc.), followed by NIR-mediated heating on days 1 and 8. Up to four lesions per patient were treated, with intratumoral temperatures maintained at 42–48 °C for 5 minutes. Safety, feasibility, and early biological responses were evaluated through adverse-event monitoring, clinical photography, and tumor biopsies obtained on days 15 and 29.

Results: Preclinical Mouse Studies: In B16F10 melanoma tumors, precisely controlled targeted hyperthermia (42–48 °C) elicited a robust 48-hour immunogenic response marked by calreticulin and HSP70 surface exposure, upregulation of antigen presenting machinery and activation of chemokine and complement cascades. Integrated transcriptomic and flow cytometric analyses revealed rapid innate immune engagement, highlighted by strong activation of the cGAS–STING pathway and enrichment of pro-inflammatory macrophages and dendritic cells. These innate responses were accompanied by enhanced T-cell activation, expansion of memory T-cell populations, and coordinated T-cell receptor clonal remodeling. Clinical: THT was well tolerated, with no treatment-related serious adverse events observed. By day 15, eight of ten patients exhibited clinical tumor regression in representative treated lesions. Complete histologic clearance was observed in six patients, partial regression in two, and no response in two patients.

Conclusion: THT demonstrates safety, feasibility, and rapid biological activity in patients with immunotherapy-refractory metastatic melanoma. Mechanistic analyses show that controlled hyperthermia induces coordinated innate and early adaptive immune activation and defines actionable parameters to guide rational combination with immune checkpoint blockade.

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Redefining the Ideal Window to Resection Following Neoadjuvant Therapy for Pancreatic Ductal Adenocarcinoma

David P. Cyr, MD, PhD, Sanjay S. Reddy, MD, Emily Kolodka, MD, Caroline Westwood, MD, Hal Rives, Joseph Krempa, Jennifer Hwang, MD, Anthony M. Villano, MD

Fox Chase Cancer Center

Introduction: Neoadjuvant treatment for pancreatic ductal adenocarcinoma (PDAC) has shifted from chemoradiation (CRT) alone to systemic regimens and total neoadjuvant therapy (TNT). We sought to define the optimal interval from completion of neoadjuvant therapy to surgery (time-to-surgery) and its effect on perioperative and oncologic outcomes in the contemporary era.

Methods: Consecutive patients undergoing pancreatectomy for PDAC between 2010–2025 after single modality neoadjuvant therapy (SMNT) or TNT were identified from a prospectively maintained database. Patients were grouped by treatment (SMNT, TNT), year of surgery (P1: 2010–2015, P2: 2016–2020, P3: 2021–2025), or time to surgery (≤4 weeks, 5–10 weeks, >10 weeks). Statistical analyses were performed.

Results: The cohort included 184 patients (SMNT n=91, TNT n=93). Use of systemic chemotherapy in SMNT rose from 21% (P1) to 83% (P2) and 98% (P3) (p10 weeks; P3: 0% ≤4 weeks versus 46% >10 weeks; p=0.0004). There were no differences in baseline patient/tumor features across time-to-surgery groups. Lastly, TNT patients with time-to-surgery ≤4 weeks had significantly worse 5-year disease free survival (12.5% [95%CI 2.0–78.2]) compared to 5–10 weeks (28.6% [17.9–45.6]) and >10 weeks (58.0% [40.9–82.3]) (p=0.01).

Conclusion: Delaying resection beyond the early post TNT period was associated with improved DFS. Further study is needed to define optimal timing of multimodal therapy and surgery in modern neoadjuvant protocols.

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Adverse Neurovascular Events Associated with Complex Pelvic Sidewall Surgery: Single-Centre Retrospective Observational Analysis

Nardin Farag, MDCM, Sameer S. Apte, MDCM, MSc, FRCSC, Kala Hickey, MD, MSc, FRCSC, Hela Kabani, BSc, Kwadjo Nyarko, Luke Lavallée, MDCM, MSc, FRCSC, Sarah Sinasac, MD, MPH, FRCSC, Amarvir Bilkhu, MB/BChir, MA, PGCE, FRCS

Faculty of Medicine, University of Ottawa

Introduction: Pelvic sidewall surgery for pelvic malignancy is high-risk and technically challenging.

Methods: Adult patients undergoing either pelvic lymph node dissection only (PLND) or curative-intent major PSWS (vascular or muscular resections or neural dissections) at The Ottawa Hospital (2022–2025) were reviewed. Predictors of 90-day neurovascular and overall complications were assessed.

Results: Of 84 patients, 65 (77.4%) underwent PLND and 19 (22.6%) major PSWS. Complications occurred in 49/84 (58.3%). Of those, 21/84 (25.0%) had major complications (Clavien-Dindo ≥3a). Neurovascular complications occurred in 15/84 (17.9%): neuropathy (9/15), venous thromboembolism (4/15), acute limb ischemia (3/15), major bleeding (3/15). Major PSWS had higher neurovascular (42.1% vs 10.8%) and major complication rates (57.9% vs 15.4%). Within 90-days, 19 patients required readmission, and 2 died. In multivariable analysis, only EBL ≥1000 mL (OR 10.20 95%CI[1.60-83.77], p=0.018) remained an independent predictor of neurovascular complications, while BMI ≥35 (OR 12.71 95%CI[1.47-153.60], p=0.027) and previous radiation (OR 41.78 95%CI[5.31-674.61], p=0.002) were independent predictors of major complications. Although major PSWS was significantly associated with major complications in univariable analysis, this association was not independently significant after multivariable adjustment.

Conclusion: Although safe in well-selected patients, neurovascular complications are an important consideration of major PSWS. Targeted pathways for thromboprophylaxis and postoperative limb monitoring are critical.

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Sodium Thiosulfate for the Prevention of Cisplatin-Induced Nephrotoxicity during HIPEC: a Meta-Analysis

Kala E. Hickey, MD, MSc, FRCSC, Nardin Farag, MDCM, Kyran Sachdeva, MD Candidate, Brittany Dingley, MD, MPH, FRCSC, Sameer Apte, MDCM, MSc, FRCSC

Department of Surgery, Faculty of Medicine, University of Ottawa

Introduction: CRS-HIPEC improves oncologic outcomes in select patients with peritoneal surface malignancies. Nephrotoxicity is a dose-limiting complication of platinum-based HIPEC. Sodium thiosulfate (STS) has been investigated as a nephroprotective agent. This is the first systematic review and meta-analysis summarizing its impact.

Methods: PubMed, Embase, and Cochrane Library were searched for studies evaluating nephroprotective agents used during platinum-based HIPEC. The primary outcome was post-operative acute kidney injury (AKI).

Results: Of 252 records screened, 23 studies were included. Seven comparative studies with STS versus no STS were identified. Cisplatin dosing was 50–100 mg/m² over 60–90 minutes. STS was associated with substantially lower odds of AKI (random-effects OR 0.08, 95% CI [0.04–0.16];

Conclusion: In comparative studies, STS was associated with significantly lower odds of AKI in patients undergoing platinum-based HIPEC. Evidence for other nephroprotective agents was limited and inconclusive. This systematic review and meta-analysis supports the use of STS during platinum-based HIPEC.

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A Watch and Wait approach after locoregional complete clinical response in Rectal Cancer: A Systematic Review

Sandra Messiha, MD, Diane Kim, Enoch Yu, Dakota Gustafason, PhD, Ameer Farooq, MD, FRCSC, Sean Bennett, MD, MSc, FRCSC

Queen’s University

Introduction: Colorectal cancer is the third most common cancer in North America. Radical surgery for rectal cancer in the form of an abdominoperineal resection or low anterior resection with total mesorectal excision is associated with significant morbidity and a 2% mortality rate. Following neoadjuvant therapy, up to 26% of patients have been found to have a complete pathological response to treatment. Therefore, the necessity of radical surgery in patients with a complete clinical response following initial therapy has been rightfully questioned. This study evaluates the current literature detailing the expected outcomes of patients with rectal cancer who have a loco-regional complete clinical response to neoadjuvant therapy and are managed with a watch-and-wait approach.

Methods: A literature search was conducted using Medline, OVID, and SCOPUS to identify papers reporting rectal cancers treated with neoadjuvant chemotherapy and/or radiation therapy wherein patients were managed with a watch-and-wait approach. 3185 studies were identified following the removal of 2635 duplicate papers. The final list of full-text review papers included 52 studies, and only prospective studies were included. Data extraction was completed by four independent reviewers using standardized data extraction forms. All disagreements were resolved by discussion. Quantitative data were then analyzed descriptively and thematically.

Results: Following full-text review, 37 papers were included in the final data analysis. Neoadjuvant therapy regimens varied between centers, specifically in the combination and sequencing of chemotherapy and radiotherapy. However, the majority of patients received concurrent chemoradiotherapy in addition to induction chemotherapy and/or consolidation chemotherapy. For patients with a complete clinical response on a watch-and-wait protocol, the one-year local recurrence rate was 13.0% (7-19%, 95% CI). The two-year local recurrence rate was 18% (12.1-23.9%, 95% CI). The two-year overall survival rate was 98.4% (96.9-99.9%, 95% CI). The five-year overall survival rate was 92.7% (88.7-96.6%, 95% CI). For patients identified as having a local recurrence, 78.4% (71.6-85.2%, 95% CI) of patients underwent salvage surgery. Lastly, 7.1% (5.3-8.9%, 95% CI) of patients developed metastatic disease during follow-up.

Conclusion: In summary, a watch-and-wait approach for rectal cancer patients following a complete clinical response demonstrates favorable long-term outcomes. Up to 18% of patients managed with watch-and-wait develop a local recurrence within 2 years.

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The Prevalence of Osteopenia in Adult Non-Metastatic Gastrointestinal Cancer Patients: A Systematic Review and Meta-Analysis

Sara Bocchinfuso, MB BCh BAO 1, Natalie G. Coburn, MD MPH 1, 2, 3, 4; Sheharzad Mahmood, MD 1, 2; Ka Yan Ip, BSS MPH 3, Natasha Barone, MD 1, 2; Cheuk See Yau, BSc 3, Leonardo R. Brandão, MD MSc 1, 5; William K Silverstein, MD MSc, 1, 6; Farhana Shariff, MDCM, MSc 7, Teresa Tiano, BA, 8, Neill KJ Adhikari, MDCM MSc 1, 9;

1 Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, 2 Department of Surgery, University of Toronto, 3 Clinical Evaluative Sciences, Sunnybrook Research Institute, 4 Odette Cancer Centre, Sunnybrook Health Sciences Centre, 5 The Hospital for Sick Children, University of Toronto, 6 Department of Medicine, University of Toronto, 7 Department of Surgery, University of Manitoba, 8 Stomach Cancer Foundation of Canada, 9 Department of Critical Care Medicine, Sunnybrook Health Sciences Centre

Introduction: Improvements in survival among patients with gastrointestinal (GI) cancer have led to a shift in focus towards management of cancer-related sequelae, including osteopenia. We aimed to estimate the global prevalence of osteopenia in adults with non-metastatic GI cancer.

Methods: We conducted a comprehensive search of multiple e-databases from January 1, 1994, to October 2, 2025, for studies of adult GI cancer patients reporting osteopenia prevalence. Paired reviewers independently screened citations, selected studies, abstracted data, and assessed study quality. Pooled prevalence was estimated using a random effect generalized linear mixed model. Certainty of evidence was assessed using the GRADE framework.

Results: 18 eligible studies (1635 patients), mostly prospective cohorts (10/18) measuring bone mineral density following completion of cancer treatment (14/18), were included. The pooled prevalence of osteopenia was 40% (95% CI 33-48%; 95% PI 16-70%, I2=88%; τ2=0.39); certainty of evidence was moderate after downgrading for risk of bias. In a prespecified subgroup analysis, osteopenia prevalence was higher in studies of gastric cancer (45%, 95% CI 39–50; 11 studies, 1,096 patients) than other GI cancers (30.6%, 95% CI 17.2–48.2; 7 studies, 539 patients; P=0.08; low-credibility subgroup effect); however, comparisons are limited by small sample size. Prevalence was 40% in a sensitivity analysis limited to low risk of bias studies (95% CI 27-54; 9 studies, 957 patients).

Conclusion: Moderate-certainty evidence suggests that the prevalence of osteopenia in adults with GI cancer is 40%. Our findings underscore the importance of bone health as a survivorship priority.

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Colorectal Signet-ring Adenocarcinoma Risk in P/LP CDH1 Variant Patients: Systematic Review

Elizabeth N. Clarke, BHSc and Matthew Benesch, MD PhD MPH FRCSC

Memorial University of Newfoundland

Introduction: CDH1 (E-cadherin) inactivation is well-established as a genetic risk factor for signet-ring cell adenocarcinoma (SRCC) in hereditary diffuse gastric cancer and lobular breast cancer in female carriers. However, recent evidence suggests colorectal SRCC (CSRCC) as a third primary cancer site in these patients. Since the gold-standard approach in CDH1 mutation carriers is prophylactic total gastrectomy, highly fatal CSRCC may now represent the limiting factor in patient lifespan.

Methods: A systematic review searched PubMed and Embase; due to the rare nature of the condition under study, no date, language or article type restrictions were imposed. Inclusion criteria required studies to have examined patients with a primary CRC diagnosis with a genetically verified CDH1 mutation and/or are part of a known CDH1 family.

Results: The defined search string plus reference scanning identified a total of 7 case series and one case report meeting the inclusion criteria for full-text review. P/LP CDH1 variants were reported in between 1.03-64% of CSRCC patients, suggesting enrichment of this very rare cancer morphology in these patients compared to ≤1% of the general population. Age at CSRCC diagnosis was reported at between 15-62 years, suggesting that P/LP CDH1 variants precipitate earlier onset of disease compared to an average of 65.2 years in the general population.

Conclusion: The present study further characterizes the association between P/LP CDH1 variants and CSRCC risk. We reinforce previous calls for future larger studies with higher statistical power. CDH1 patients may benefit from high-risk colorectal cancer surveillance.

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Co-Development of Culturally-Safe Breast Cancer Education tools for Culturally and Linguistically Diverse (CALD) Communities: A Comprehensive Review

Valentina Shamoun 1, Gayathri Naganathan 2, Mojola Omole 3, Anna Dare 4, Andrea Covelli 4, Sheharzad Mahmood 5, 6; Areeba Chaudhry 1, Elias Djemai 6

1 Temerty Faculty of Medicine, University of Toronto, 2 Division of General Surgery, Department of Surgery, Michael Garron Hospital, 3Division of General Surgery, Department of Surgery, Scarborough Health Network, 4 Division of Surgical Oncology, Department of Surgery, St. Michael’s Hospital, 5 Division of General Surgery, Department of Surgery, University of Toronto, 6 Institute of Policy, Evaluation and Management, Dalla Lana School of Public Health, University of Toronto

Introduction: BACKGROUND: Culturally safe patient education is essential throughout the breast cancer care continuum to facilitate shared decision making and to improve clinical and patient-reported outcomes. However, existing breast cancer educational interventions for culturally and linguistically diverse (CALD) populations have largely emphasized screening and early detection, with limited attention to diagnosis, treatment, and survivorship. CALD patients also remain underrepresented in research evaluating decision aids and educational tools, despite experiencing additional barriers to accessing breast cancer care contributing to worse outcomes. This gap is particularly relevant in Toronto, Ontario, where 55.7% of residents identify as racialized- the highest proportion in Canada. Developing culturally relevant, locally informed resources is therefore critical to achieving equitable breast cancer care.

OBJECTIVE: To map the current global evidence on culturally tailored breast cancer education tools for CALD populations to identify strategies, gaps, and methodologic frameworks that will inform the future co-development of locally relevant education resources for diverse communities in Toronto, Ontario.

Methods: A narrative review was conducted using Scopus and MEDLINE (search date: July 2025; timeframe: 2000-present) to identify relevant studies using search terms related to “breast cancer” and “education” and “cultural”. Eligible studies included breast cancer patients at or beyond diagnosis (screening only studies excluded) and incorporated cultural tailoring or co-development. Data extraction captured educational content, phase of care (diagnosis, treatment, survivorship), cultural tailoring strategies, delivery formats, co-design methods, and reported outcomes. ‍

Results: Of 1,273 articles screened, 17 met inclusion criteria. Most studies originated from the United States (64.7%) or China (11.7%), with single studies from Portugal, Jordan, Canada, and Australia. Target populations most represented were Hispanic/Spanish-speaking (41.2%), East Asian (35.3%), and Arabic-speaking (11.8%) communities, with some studies addressing multiple groups.

Educational interventions addressed diagnosis (23.5%), treatment (52.9%), and survivorship (58.9%), with several spanning multiple phases of care.   Formats included patient navigation programs, support groups, videos, and educational modules (slides, lectures, brochures).  Reported benefits included improved knowledge and awareness of breast cancer, timeliness of care, communication with care providers, and cultural acceptability. Common cultural tailoring strategies involved community advisory boards, collaboration with advocacy organizations, and use of focus groups. Key barriers to delivery of culturally safe education included financial and staffing constraints, cultural and language discordance, limited patient awareness about available care options, and systemic challenges. Additionally, psychosocial factors such as fear, stigma, and limited social support were prevalent and further limited participation, yet their manifestations differed by cultural context. Differences in cultural gender norms, religious beliefs, and family dynamics across communities were also emphasized as influencing education needs, underscoring the need for further culturally nuanced and responsive approaches.  Heterogeneity in study design and evaluation methods limited comparisons and long-term outcome assessment.

Conclusion: Culturally tailored and patient-centered breast cancer education interventions enhance understanding, trust, and engagement in care amongst CALD patients. Integrating cultural and linguistic adaptation into breast cancer care pathways may strengthen shared decision making and reduce disparities in care.  

This review provides strategies and highly actionable approaches for breast cancer clinicians to bridge cultural and linguistic gaps in patient education. The findings directly inform ongoing community-engaged research in Toronto aiming to translate these findings into a local needs assessment and co-developed educational tool that reflects the needs, values, and preferences of CALD patients and their families to support equitable and culturally safe breast cancer care.

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Environmental Sustainability in Multidisciplinary Breast Cancer Care: A Scoping Review of Current Practices and Opportunities

Amanda Mac, MD 1, Adam Fontebasso, MD 2, Christine Lam, MSc 3, Janet Tang, MD 1, Ela Howard 4, Emma Reel, MSW 5, Marina Englesakis, MLIS 6, Tulin Cil, MD Med 5

1 Division of General Surgery, Department of Surgery, University of Toronto, 2 Department of General Surgery, Hôpital Pierre-Boucher, 3 Temerty Faculty of Medicine, University of Toronto, 4 Faculty of Applied Science and Engineering, University of Toronto, 5 Division of General Surgery, Department of Surgery, Princess Margaret Cancer Centre – University Health Network, 6 Library and Information Services, University Health Network

Introduction: Breast cancer is the most common cancer affecting women and is second in female cancer-related mortality. The treatment of breast cancer is multidisciplinary and can be resource intensive. We aimed to characterize the environmental impact of breast cancer care and highlight opportunities for reducing its ecological footprint.

Methods: MEDLINE, MEDLINE In-Process/ePubs, Embase, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews were searched using terms related to breast cancer and environmental impact. The search strategy was run from inception to October 11, 2023, and updated on July 17, 2025. Peer-reviewed records that discussed the environmental impact of breast cancer care practices were included.

Results: The search identified 6772 articles from which 36 were included for review. The environmental impact of breast cancer care can be reduced through waste-minimizing surgical practices, renewable energy use and streamlined pathology methods. In radiation therapy, hypofractionation, telemedicine and intraoperative radiation reduce emissions from travel and energy consumption. Sustainable approaches to chemotherapy production include renewable energy, metabolic engineering and CRISPR/Cas9 technologies. Telemedicine and alternative dosing strategies can similarly reduce the carbon footprint of immunotherapy. In breast cancer research and clinical trials, sustainability may be enhanced through virtual engagement, renewable energy adoption and inclusion of environmental outcome measures.

Conclusion: We outline the environmental impact of current practices across the continuum of breast cancer care. Our findings will inform recommendations for transforming our healthcare system into one that is sustainable and capable of offering high-quality care to future generations of patients with breast cancer.

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Establishing patient-derived gastric cancer organoids from endoscopic and surgical specimens for personalized drug testing

Shelly Luu, MD PhD FRCSC 1, Karineh Kazazian, MD, PhD, FRCSC 2, Karina Pacholczyk, BSc 3, Ning Fu, MD 4, Yvonne Bach, MSc 2, Nikolina Radulivich, PhD 2, Sangeetha Kalimuthu, FRCPath, FRCPC 2, James Conner, MD, PhD, FRCPC 5, Elena Elimova, MD, FRCPC 2, Fayez Quereshy, MD, MBA, FRCSC 2, Jonathan Yeung, MD, PhD, FRCSC 2, Carol Swallow, MD, PhD, FRCSC 5

1 University of Toronto, 2 University Health Network, 3 Lunenfeld-Tanenbaum Research Institute, 4 McMaster University, 5 Sinai Health System

Introduction: Gastric adenocarcinoma (GAC) is a biologically heterogeneous disease with limited actionable molecular targets in the perioperative setting. Reliable, patient-specific preclinical models are lacking. Patient-derived organoids (PDOs) offer a promising ex vivo platform to model tumor biology and therapeutic response. We developed and optimized a protocol to establish GAC PDOs from both untreated endoscopic biopsies and resection specimens, enabling drug testing in clinically relevant timeframes.

Methods: Between April 2024-August 2025, with institutional REB approval and patient consent, tumour samples were collected from patients undergoing upper endoscopy (EGD) or curative gastrectomy. PDOs were generated using a standardized culture protocol that we developed, and characterized by histology, short tandem repeat (STR) profiling, SNP and whole genome sequencing. Drug sensitivity screens were performed using clinically relevant chemotherapeutic and targeted agents and compared to patient outcomes derived from a prospectively maintained GAC patient database.

Results: Eighteen PDOs were established from 30 gastric tumour samples (60% success rate), with failure more common when patients had received prior treatment. Of the 18 PDO lines, 9 were derived from 15 endoscopic biopsy specimens and 9 from 15 gastrectomy specimens, demonstrating feasibility in both settings. Based on H&E staining, the organoids accurately mimicked the histologic architecture of the individual patient tumour from which they were derived. Furthermore, PDO lines recapitulated the parental tumour’s genomic profile (mean STR overlap ~80%, n=4). Drug screens revealed distinct ex vivo responses to individual agents that mirrored the corresponding patient’s clinical response.

Conclusion: We demonstrate feasibility of generating patient-matched GAC PDOs from both endoscopic biopsy and surgical specimens. These PDOs retain key histologic and molecular features of the original tumor and exhibit concordant therapeutic responses. This platform provides a clinically relevant model for studying GAC biology, testing therapeutic sensitivity, and advancing precision oncology strategies in GAC.

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Primary Tumor Sites in Signet-Ring Cell carcinoma (SRCC) Metastasis to the Breast: A Rapid Review

Mayar Elbaz, PGY2 Medical Student 1, 2; Matthew Benesch, MD PhD MPH FRCSC 1, 3, 4, 5, 6;

1 Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, 2 Memorial University of Newfoundland, School of Medicine, 3 Department of Surgery, University of Toronto, 4 Clinical Evaluative Sciences, Sunnybrook Research Institute, 5 Odette Cancer Centre, Sunnybrook Health Sciences Centre, 6 Memorial University of Newfoundland, NL Health Services

Introduction: Signet-ring cell carcinoma (SRCC) is a rare, dedifferentiated variant of adenocarcinoma, most commonly originating in the gastrointestinal tract. While the stomach and colon are the most frequently reported primary sites, SRCC can arise in various locations including the pancreas, appendix, and bladder. Metastasis to the breast is exceptionally rare and frequently mimics primary breast cancer, creating diagnostic and therapeutic challenges. A comprehensive synthesis of primary tumor sites in breast metastasis is lacking.

Methods: A rapid systematic review was conducted. PubMed, Embase, and Scopus were searched without language or publication-type restrictions. Case reports and case series reporting extramammary SRCC with pathologically confirmed breast metastasis were included. Title/abstract screening and full-text review were completed using Covidence, and data regarding primary tumor sites and study characteristics were extracted.

Results: The database search identified 486 records, of which 248 unique studies were screened after duplicate removal. Full-text review was conducted for 31 studies, with 28 meeting inclusion criteria. A primary SRCC of the breast accounts for 0.03% of breast cancers while most are metastases. The most frequently reported primary tumor site was gastric (~68%), followed by colorectal (~21%). Less commonly reported origins included the appendix (~7%), and the urinary bladder (~4%). The literature was dominated by individual case reports and small case series, reflecting the rarity of this metastatic pattern.

Conclusion: A diagnosis of breast SRCC should prompt investigation for an alternate primary source, particularly gastric or colorectal. Awareness of these metastatic patterns may facilitate prompt appropriate evaluation and management.

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Survival Benefit of Neoadjuvant Chemotherapy in Borderline Resectable Pancreatic Cancer

Sydney Brandt MD MSc 1, Kenneth Leslie MD 1, Evelyn Waugh MD MPH 1, Daniel Breadner MD MSc 2, Rachel Liu MD 1, Ephraim Tang MD, MSc 1, Laura Allen, MD, MSc 1, Stephen Welch MD 1, Anton Skaro MD 1

1 Department of Surgery, Division of General Surgery, Western University, 2 Department of Oncology, Division of Medical Oncology, Western University

Introduction: Recurrence following pancreatic cancer resection is often systemic, suggesting occult metastatic disease is present on presentation. Morbidity post operatively can delay systemic treatment, worsening survival outcomes. Guidelines surrounding the use of neoadjuvant chemotherapy (NAC) are varied and open to interpretation. This study examines the survival benefit and oncological outcomes of NAC prior to surgical resection in borderline resectable pancreatic cancer (BRPC).

Methods: PubMed, Embase, and Cochrane Library were searched for studies evaluating nephroprotective agents used during platinum-based HIPEC. The primary outcome was post-operative acute kidney injury (AKI).

Patients with BRPC defined by AHPBA criteria and/or Ca19-9 level >100u/ml were drawn from a prospectively populated institutional registry from 2007-2023. Patients underwent upfront surgery (US) or received NAC prior to proceeding with surgical resection (NAC-S).  Variables including overall and disease-free survival, margin status, lymph node positivity, and post-operative complications were assessed. A Cox Proportional Hazard model based on intention to treat was used to assess survival.

Results: Of 222 patients with BRPC, 158 proceeded to surgery. The remaining 64 received NAC but were then deemed unfit due to disease progression or worsening health status. Of those taken to surgery, 81 received NAC and 77 US. At 1 year, 11.1% of NAC-S patients versus 52.6% of US patients were deceased

Conclusion: Neoadjuvant chemotherapy in the management of BRPC provides patients with a survival benefit and prolongs survival time post-operatively. Surgical outcomes are improved through a reduction in lymph node positivity and improved R0 resection status.

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Pre-diagnostic delays for symptomatic breast cancer in Canada: A scoping review using an ecological framework

Sheharzad Mahmood, MD 1, 2; Anna Dare, MBChB PhD FRCSC 1, 2, 3; Sara Bocchinfuso, MB BCh BAO 2, 4; Teruko Kishibe, MISt 5

1 Division of General Surgery, Department of Surgery, University of Toronto, 2 Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, 3 Division of General Surgery, Department of Surgery, St. Michael’s Hospital, 4 Division of General Surgery, Department of Surgery, Mayo Clinic, 5Li Ka Shing Knowledge Institute, St. Michael’s Hospital

Introduction: Breast cancer patients in Canada who present symptomatically may experience diagnostic pathways marked by delays and poorer outcomes. We conducted a scoping review examining how delays in symptomatic breast cancer diagnosis are conceptualized and measured in Canada, and to identify key determinants and explanatory frameworks underlying variation. We defined the pre-diagnostic interval (PDI) as the time between symptom onset and breast cancer diagnosis.

Methods: We performed a comprehensive search of MEDLINE, EMBASE, CINAHL, PsycINFO, Web of Science, and grey literature from January 1, 2000-December 9, 2025 for studies that quantitatively or qualitatively measured PDIs for symptomatic breast cancer. Findings were synthesized narratively and mapped across 4 ecological domains.

Results: Of 2365 records identified, 38 studies were included. Substantial heterogeneity was observed in PDI measurement and definitions of delay. Quantitative studies (n=30/38) predominantly relied on administrative proxies to define symptomatic presentation and most commonly evaluated the index health system contact/imaging-to-pathological diagnosis interval (median range 9-68 days). Determinants of delay were largely identified at health-system and structural levels including geographic variation, lack of organized diagnostic pathways, and access to navigation programs. Qualitative studies (n=8/38) more often captured individual and interpersonal determinants of symptom-to-first presentation delay, including symptom normalization, competing priorities, and sociocultural factors.

Conclusion: PDI delays are common among patients with symptomatic breast cancer in Canada but are predominantly conceptualized as post-presentation, system-level intervals. This underestimates total delay and obscures critical upstream factors shaping access to care. Reframing PDI delay using an ecological lens may better inform equitable, patient-centred approaches to improving cancer diagnostic pathways.

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Association between body mass index and treatment outcomes among women with breast cancer at a Canadian tertiary care centre: results from a prospective cohort study.

C. Penny, MD 1, A. Drohan, MD, MSc, FRCSC 1, 2; H. Stewart, MSc 2, R. Hemsworth, BSc 2, A. Mayo, MD PhD 2, G. Knapp; MD, MSc, FRCSC 1, 2

1 Division of General Surgery, Dalhousie University, 2 Breast Health Research Unit, IWK Women and Children’s Hospital

Introduction: Obesity is an established risk factor for breast cancer. An elevated BMI has also been linked with adverse clinical outcomes, including larger tumor size, higher tumor grade, and a greater propensity toward node-positive disease. This study sought to characterize the relationship between BMI and breast cancer outcomes at a Canadian tertiary care centre.

Methods: Participants were classified into 3 groups according to BMI: normal weight (<25 kg/m2), overweight (25–29.9 kg/m2), and obese (≥30 kg/m2). Outcomes included detection by screening mammogram, disease stage, and treatments received (surgery, adjuvant chemotherapy, and adjuvant radiotherapy). Data were analyzed with chi-square test; for outcomes significant at the univariate level, bivariate and multiple logistic regression analyses were conducted.

Results: A total of 781 participants were included, the majority of whom were overweight (253/781, 32.4%) or obese (332/781, 42.5%). Diagnosis by screening mammogram was more common among overweight (OR=1.50, 95% CI 1.03–2.18) and obese patients (OR=1.59, 95% CI 1.11–2.26) compared to those with normal BMI. The majority of patients (546/784, 69.6%) underwent breast-conserving surgery (BCS). Women in the obese BMI category had decreased odds of undergoing mastectomy (OR=0.68, 95% CI 0.46–0.99). Obese patients were more likely to receive adjuvant radiotherapy (OR=1.79, 95% CI 1.22–2.63), though this was explained by surgery type, margin positivity, and nodal status in multivariate analyses (aOR=1.45, 95% CI 0.76–2.78, p=0.15).

Conclusion: This study documented increased odds of breast cancer detection by screening mammogram among obese women, highlighting the importance of screening mammograms in this patient population.

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Current Practices and Yield of Diagnostic Peritoneal Lavage:  A Survey of Canadian Gastric Cancer Surgeons

Daniel Skubleny, MD, PhD 1, Trevor Hamilton, MD, MSc 1, Erika Schmitz, MD 1, Farhana Shariff, MD, MSc 2

1 University of British Columbia, 2 University of Winnipeg

Introduction: Diagnostic staging laparoscopy with peritoneal lavage (DPL) is an essential strategy to identify radiologically occult peritoneal metastasis in gastric cancer. While staging laparoscopy is widely used, considerable variation exists in its indications and technical execution. This study aims to characterize contemporary Canadian practice patterns for staging laparoscopy and DPL for gastric cancer.

Methods: A national, web-based survey was distributed to Canadian gastric cancer surgeons affiliated with the Canadian Society of Surgical Oncology. The survey assessed indications for staging laparoscopy, DPL technique, degree of anatomic assessment, cytologic methods, and surgeon demographics. Responses were summarized using descriptive statistics, with subgroup comparisons by Complex General Surgical Oncology (CGSO) fellowship training status.

Results: Twenty-three surgeons responded. Routine DPL was performed by 83% of respondents, most commonly for ≥T2 disease. Substantial heterogeneity was observed in DPL indications and technique, including the timing of biopsy relative to lavage, the volume of instilled and retrieved fluid, aspiration sites, and port placement.

Conclusion: There is marked heterogeneity in the indications and technique of staging laparoscopy and DPL among Canadian gastric cancer surgeons. Given the prognostic importance of peritoneal disease detection, these findings highlight the need for standardized, evidence-informed national guidelines and provide a foundation for clinical care and prospective research.

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Nodal burden among patients with lobular breast cancer who meet SOUND and INSEMA trial eligibility for sentinel lymph node biopsy omission

Nebojsa Oravec, MD 1, Alison Laws, MD, MPH 2, Alynne Ribano, MD, MSc 1, Flora Yang, MDSA, Meng 3, May Lynn Quan, MD, MS 1, Lisa Barbera 4, Omar F. Khan, MD, MBA 4

1 Department of Surgery, University of Calgary Cumming School of Medicine, 2 Departments of Surgery and Oncology, University of Calgary Cumming School of Medicine, 3 Arthur Child Comprehensive Cancer Centre, 4 Department of Oncology, Division of Radiation Oncology, University of Calgary Cumming School of Medicine

Introduction: The SOUND/INSEMA trials proved the safety of sentinel node biopsy (SNB) omission for small cN0 breast cancers. Invasive lobular cancer (ILC) was underrepresented and often has higher nodal burden, so uncertainty remains whether findings are generalizable to ILC.

Methods: We queried the Alberta Cancer Registry (2017–2022) for patients with ILC and characteristics reflective of real-world SOUND/INSEMA application: postmenopausal aged 50-75, cT1-2 c/iN0, ER+ HER2- and undergoing lumpectomy. During this timeframe, SNB was routine. We determined rate and predictors of nodal metastases (pN+).

Results: 456/466 (97.9%) eligible patients had SNB and were included. Nodal metastases were identified in 46 patients (10.1%, 95%CI 7.6-13.2%): 2.9% were pN1mi, 6.8% were pN1 and 0.4% were pN2-3. Preoperative factors associated with pN+ were cT size (1-10mm: 5.2%, 11-20mm: 10.9%, 21-30mm: 15.1%, >30mm: 26.3%, p=0.007) and LVI on biopsy (38.5% vs. 9.3%, p=0.001). Both remained significant in multivariable analysis. Postoperative pathologic factors associated with pN+ were pT size (1-10mm: 2.6%, 11-20mm: 8.4%, 21-30mm: 19.8%, >30mm: 20.9%, p20%.

Conclusion: Overall pN+ rate for ILC was in-line with SOUND/INSEMA trials. We suggest SNB omission for cT1 ILC without LVI on biopsy; pT2 or LVI on surgical pathology may warrant return for SNB.

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Survival following neoadjuvant systemic therapy vs. upfront surgery for T1c and T2 HER2-positive and triple-negative breast cancers between 2010–2022: A retrospective SEER database cohort study

Yerin R. Lee, BHSc 1, 2; Vasily Giannakeas, PhD 2, 3; David W. Lim, MDCM MEd PhD 1, 2 ,3

1 Temerty Faculty of Medicine, University of Toronto, 2 Women’s College Research and Innovation Institute, Women’s College Hospital, 3 Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto,

Introduction: Neoadjuvant systemic therapy (NST) is standard of care for HER2-positive (HER2+) and triple-negative breast cancers ≥20 mm or with nodal involvement. However, the survival implications of treatment sequencing in early-stage disease, particularly T1c tumors, remain uncertain. We evaluated the association between NST and upfront surgery with overall survival (OS) across T1c–T2 HER2+ and triple-negative breast cancer.

Methods: We conducted a population-based retrospective cohort study using the Surveillance, Epidemiology, and End Results (SEER) database (2010–2022). OS was analyzed using Kaplan-Meier analysis, multivariable Cox regression, and inverse probability of treatment weighting (IPTW). Analyses were stratified by tumor size, nodal status, and hormone receptor subtype.

Results: Among 76,523 patients, 61.5% underwent upfront surgery and 38.5% received NST. In T1c triple-negative breast cancer, upfront surgery was associated with improved OS

Conclusion: Upfront surgery was associated with improved long-term OS in patients with T1c triple-negative breast cancer (but no difference for T2), whereas NST was associated with improved OS in T2 and node-positive HER2+ disease (but not T1c) disease.

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Polarimetry assessment of breast cancer core biopsies: can it predict the status of sentinel lymph nodes?

Kseniia Tumanova, PhD candidate 1, Mohammadali Khorasani, MD 2, Sharon Nofech-Mozes, MD 3, Alex Vitkin, PhD 1

1 Department of Medical Biophysics, University of Toronto, 2 Department of Surgery, University of British Columbia, 3 Department of Laboratory Medicine and Pathobiology, University of Toronto

Introduction: Sentinel lymph node (SLN) biopsy plays a key role in prognostication and treatment decision-making in breast cancer (BC) but is an invasive procedure with added risks and possible side effects for the patient. Mueller matrix polarimetry (MMP) is a label-free optical technique that quantifies tissue biophysical properties and may reveal microstructural features associated with nodal metastatic potential. This study evaluates whether polarimetric features extracted from diagnostic core biopsies can predict SLN status in BC.

Methods: Polarimetric imaging was performed on unstained sections from diagnostic core needle biopsies obtained from primary tumour of 68 patients with ER+ / HER2– invasive BC (27 patients had SLN metastasis, while 41 had no nodal involvement). From each case, thirty polarimetric features were extracted from the entire tissue section. A supervised random forest model was trained using polarimetric features to classify SLN status. Model performance was evaluated using five-fold cross-validation and an independent test set. Metrics included area under the receiver operating characteristic curve (AUC), average precision, sensitivity, specificity, and accuracy.

Results: The machine learning model achieved a mean AUC of 0.79 ± 0.15 and average precision of 0.81 ± 0.08 during cross-validation. Analysis on the previously unseen independent test set with this model reached an AUC of 0.87, average precision of 0.85, sensitivity of 0.75, specificity of 0.92, and accuracy of 0.86.

Conclusion: ML-based prediction models demonstrate promising performance, yet their practical applicability might be constrained by low interpretability and reduced generalization.

Polarimetric features from diagnostic biopsy sections may offer a non-invasive approach to predicting SLN metastasis. These findings support further investigation of MMP as a potential adjunct to early axillary risk assessment and surgical decision-making.

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Application of Machine Learning Approach to Predict Colorectal Cancer Recurrence: A Systematic Review

Vahid Mehrnoush, MD 1, Jessica A. Holland, MD 1, Laura E.Kerr, MD 1, Dhruv Lalkiya, Hbsc, MA 2, Fatemeh Darsareh, PhD 3

1 NOSM University, 2 Thunder Bay Regional Health Research Institute, 3 Hormozgan University of Medical Sciences

Introduction: Identifying risk factors associated with the recurrence of colorectal cancer (CRC) can be difficult. Progress in machine learning (ML) has led to the development of promising real-time models for predicting CRC recurrence. Therefore, we evaluated their performance through a systematic review.

Methods: A comprehensive search was conducted from Jan 1970 until Nov 2024 utilizing the subsequent inclusion criteria: 1) research that developed or validated statistical model(s) employing time-to-event data to forecast CRC recurrence in patients undergoing surgical resection; 2) research featuring at least two predictors; 3) research that provided a quantitative assessment of any element of model performance. Abstracts from conferences, along with editorials and commentaries, were excluded. Risk of bias assessment was conducted through Checklist for critical Appraisal and data extraction or systematic Reviews of prediction Modelling Studies (CHARMS).

Results: Preliminary exploration resulted in 917 articles. After eliminating duplicates, 185 articles were left for thorough screening, resulting in the inclusion of nine articles involving 11,296 patients. The recurrence rate ranged between 13.2% and 77.9%. Fourteen different ML models were used. Area under the curve (AUC), accuracy, specificity, and F1 Score were the most utilized metrics for evaluating the performance of ML models. Support vector machines, Logistic regression, Gradient boosting model, Decision tree, Artificial neural network, and CatBoost, had a better performance than the other models. The accuracy varied between 0.73 and 0.88, while the AUC ranged from 0.67 to 0.96. Age, male gender, pathologic tumor stage, pathologic tumor-node-metastasis stage, and receiving chemotherapy were identified as the top significant predictors of CRC recurrence.

Conclusion: ML-based prediction models demonstrate promising performance, yet their practical applicability might be constrained by low interpretability and reduced generalization.

The impact of intraoperative digital specimen mammography on surgical resections in total mastectomies: a single center retrospective analysis
Yasmin E. Osman, MD 1, Erica Patoscskai, MD, FRCSC 1, Brandon Noyon 2, Justin Colivas 2, Camille Gervais 3, Giancarlo Sticca, MD 1, Michael Schaulin 2, Teng Yi Huang 2, Simon Elkouri 4, Magali Caron 2, Florence Bénard, MD 1, Rim Abdelli 4, Yekta Soleimani 1, Léamarie Meloche-Dumas, MD 1, Ahmad Kaviani, MD, FRCSC 1, Kerianne Boulva, MD, FRCSC 1, Rami Younan, MD, FRCSC 1, Saima Hassan, MD, PhD, FRCSC 1, Mona El-Khoury, MD 5.

1 Centre Hospitalier de l'Université de Montréal (CHUM), Department of Surgery - Surgical Oncology Service, Montreal, Canada; 2 Université de Montréal, Faculty of Medicine, Montreal, Canada'; 3 McGill University, Faculty of Medicine, Montreal, Canada; 4 Université Laval, Faculty of Medicine, Québec, Canada; 5 Centre Hospitalier de l'Université de Montréal, Department of Radiology, Montréal, Canada.

Introduction: Achieving negative margins is critical in breast cancer surgery. While total mastectomies result in fewer positive margins compared to breast-conserving surgeries (BCS), they still occur. Intraoperative digital specimen mammography (IDSM) enables real-time evaluation of residual disease at the excised tissue edges, allowing for immediate re-excision when necessary. However, its utility in total mastectomies has not been evaluated. This study aimed to assess its relevance in this context.

Methods: A retrospective analysis was conducted at a Canadian tertiary care center, including patients diagnosed with breast cancer from 2018 to 2023 who underwent total mastectomies. The primary outcome was the accuracy with which IDSM guided appropriate management, defined as guiding re-excision when margins were positive or close (≤2mm), or when biopsy markers were absent, and confirming when re-excision was unnecessary. Fisher’s exact test was employed to identify associations between categorical variables.

Results: A total of 209 patients were included. Among 25 specimens identified as having radiologically positive margins, close margins, or missing biopsy markers, 19 (76.0%) were true positives. In comparison, there were 53 (28.8%) false negatives among the 184 radiologically negative patients (OR 7.74, 95% CI 2.78-25.03, P<0.01). IDSM demonstrated a specificity of 95.6% (95% CI 91.0%-98.0%). Moreover, among 18 radiologically positive specimens for close or positive margins, the intraoperative re-excision margin rate was 66.7% (12/18), compared to 22.7% (30/132) in radiologically negative specimens (OR 6.69, 95% CI 2.11-23.68, P<0.01).

Conclusion: IDSM could assume a pivotal role in guiding management decisions intraoperatively, thereby potentially decreasing reintervention rates.

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The influence of age on patient presentation and post-adrenalectomy morbidity for patients with pheochromocytoma: An international multicenter analysis

Sukhdeep Jatana, MDCM 1, Alessandro Parente MD, PhD 2, Kevin Verhoeff, MD, PhD 1, Robert P. Sutcliffe MS, MD 2, International Pheo Study Group

1 University of Alberta, Edmonton, Alberta; 2 Department of Hepatopancreatobiliary and Liver Transplant Surgery, Queen Elizabeth Hospital, Birmingham, UK;

Introduction: Postoperative morbidity following pheochromocytoma adrenalectomy carries a unique risk profile, and the impact of age on postoperative morbidity has been studied mostly in small cohorts.

Methods: This study aims to compare presentation and tumor characteristics stratified by age of presentation and assess the impact of age on postoperative morbidity by stratifying patients undergoing adrenalectomy for pheochromocytoma into three age groups, ≤40, 41-59, ≥60.

Results: Of 2087 patients from 46 centers, 493 were ≤40 years (23.6%), 881 between 41 and 59 years (42.2%), and 713 were ≥60 years (34.2%). Younger cohorts were more likely to have a genetic predisposition (≤40 years 30.4% vs ≥60 years 6.0%, p<0.001), bilateral tumors (8.4% vs 2.3% vs 1.1%, p<0.001), and local invasion (22.4% vs 35.6% vs 12.5%, p<0.001). Multivariate analysis showed decreased risk of all complications with older cohorts (adjusted odds ratio (aOR) 0.55, p=0.002 and 0.68, p=0.091 for 41-59 and ≥60 years versus ≤40 years), but this was not significant on analysis of severe complications (classified as CDC grade ≥3a complications; aOR 0.77, p=0.400 and aOR 0.84, p=0.636, respectively)

Conclusion: Age significantly impacts presentation of patients with pheochromocytoma, with younger patients having larger, more invasive tumors and older patients being more comorbid. However, age does not seem to a significant contributor to postoperative morbidity, with more sensitive analyses not showing significance.

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Outcomes of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS & HIPEC) and liver-directed therapy for synchronous peritoneal and liver metastatic colorectal cancer - a systematic review with meta-analysis

Simarpreet Ichhpuniani, MD 1, Antoine Bouchard-Fortier, MD 2, Kadhim Taqi, MD 2, Cecily Stockley, MD 2, Golpira Elmi Assadzadeh, PhD 1, Elijah Dixon 3, Lloyd Mack, MD 2

1 Department of Surgery, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; 2 Division of Surgical Oncology, Department of Oncology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada; 3 Division of Hepatobilliary and Pancreatic Surgery, Department of Surgery, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada

Introduction: Cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) has survival benefits in colorectal cancer (CRC) patients with peritoneal carcinomatosis (PC). The presence of synchronous liver metastases (LM) often precludes patients from CRS/HIPEC. Multiple studies suggest that CRS/HIPEC with liver-directed treatments may be beneficial. This systematic review examines outcomes and selection factors in CRC patients with PC and LM metastases treated with CRS/HIPEC and liver directed treatment.

Methods: A systematic review and meta-analysis were performed using PubMed, EMBASE and Web-of-Science from 2009 to 2024. The outcomes included potential selection factors, overall survival (OS) and disease-free survival (DFS).

Results: 482 articles were retrieved, with seventeen retrospective studies meeting criteria, with 988 patients. Liver-directed therapy with CRS/HIPEC for PC and LM was associated with 1-year, 3-years, and 5-years OS rates of 88%, 47%, and 31%, respectively, with a median survival range of 15.3–47.6 months. The 1-year and 3-years DFS were 46% and 20%, respectively, with a median DFS range of 6.2-29.4 months. Patients were more likely to have received preoperative systemic therapy (86%), underwent minor liver resection (90%), had a limited burden of LM (mean 3 lesions, median size 1.4-3 cm), and PC (mean PCI 13).

Conclusion: This study indicates that CRS/HIPEC with liver-directed therapy can yield favorable survival outcomes for well-selected CRC patients with limited PC and LM, though further trials are needed to confirm its efficacy and refine optimal patient selection.

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Patterns of referral for consideration of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for patients with peritoneal carcinomatosis of colorectal origin in Alberta, Canada

Nebojša Oravec, Cecily Stockley, Jay Lee, Kadhim Taqi, Philip Ding, Ned Liu, Winson Cheung, Lloyd Mack, Antoine Bouchard-Fortier

University of Alberta

Introduction: Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) offers a survival benefit over chemotherapy alone for select patients with peritoneal carcinomatosis (PC) of colorectal origin. This retrospective cohort study assessed patterns of referral for consideration of CRS/HIPEC in Alberta.

Methods: Patients diagnosed with T4a/b colon cancer between 2018-2023 who developed PC were identified from a review of the Alberta Cancer Registry (ACR). Data from the ACR and electronic medical records (EMR) were analyzed using descriptive statistics, Kaplan-Meier survival curves, and Cox multivariate regression.

Results: Of 791 patients with T4a/b colon cancer, 52 (6.57%) developed PC, and 26 of these patients (50.0%) were referred to a peritoneal malignancy program. Fourteen patients were offered surgery: nine successfully underwent CRS/HIPEC, three had an alternative palliative procedure, and two had surgery aborted. Among non-referred patients (n = 26), 10 (38.5%) had no apparent contraindications to CRS/HIPEC based on EMR review. Referred patients had median overall survival of 33.80 months (95% CI 0.70-40.24) vs. 10.04 months for non-referred patients (95% CI 0.18-6.59), p <0.01. There were no apparent patient or disease-related variables associated with greater odds of referral (i.e., age, year of diagnosis, rural vs urban residence, AJCC stage, lymph node status, adjuvant chemotherapy, adherence to surveillance protocols, ASA score).

Conclusion: Half of all patients with PC of colorectal origin in Alberta were not referred for consideration of CRS/HIPEC, despite referral being associated with improved survival. Optimizing referral pathways may improve patient outcomes.

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Why Don’t They Want to Wear Sunscreen? Quantifying Anti-Sunscreen Messaging on TikTok

Nina Morena, MA 1, Ari N. Meguerditchian, MD, MSc, FRCS, FACS 2, Carla Herman 1, Nathalie Harb 3, Meghri Ghazarian 4, Eric Belzile 2

1 McGill University; 2 St Mary's Research Centre; 3 Université de Sherbrooke; 4 Concordia University

Introduction: The incidence of melanoma among younger patients is increasing at an alarming rate. This demographic often turns to social media, particularly TikTok, for information, shared experiences, and connection. The emergence of anti-sunscreen messaging on TikTok is concerning. This study aims to quantify the prevalence of anti-sunscreen sentiments on TikTok and analyze their content and communication style.

Methods: Videos tagged #nosunscreen on TikTok were collected in 07/24. Reviewers gathered video characteristics such as username, user profile (individual or organisation), date posted, captions, length, number of followers, likes, views, shares, and comments, presence of sponsorship, and filming location. User demographics were noted. Reviewers also noted communication styles and other video characteristics such as the use of audio memes or music. Users’ opinions about not wanting to wear sunscreen were collected and analysed. Spearman’s correlation coefficient, Chi-squared test, and Phi coefficient was calculated between variables.

Results: 321 English language TikToks were selected. The majority (38%) were posted in 2023. Average video length was 25 seconds. Mean number of followers was 90,053 (SD 32,4640). Mean number of views, likes, and comments was 73,121 (SD 408,245), 380,800 (SD 5,250), and 51 (SD 203), respectively. 12 videos included product sponsorship. Female (78%) predominance was observed. Half of creators appeared to be younger than 25 years old. 45% of videos used music and 30% used audio memes. 32% were filmed outdoors, mostly in one’s backyard or at the beach. In 44% of videos, a sunburn was being shown. In half of the videos (49%), sunscreen sentiments were clearly described. Common reasons for not wanting to wear sunscreen include personal preferences (regarding trends), perceived benefits of natural sun exposure, sunscreen being viewed as unnecessary and/or harmful, choosing alternative forms of sun precaution, and the desire to tan. Believing it is cool/funny to be sunburnt is associated with having a reason to be anti-sunscreen, particularly the desire to tan. TikToks which convey irony and/or sarcasm (16%) are strongly associated with believing in the benefits of natural sun exposure and with choosing alternative forms of sun precaution.

Conclusion: TikTok videos tagged with #nosunscreen highlight the alarming prevalence of anti-sunscreen sentiments. Younger people are exposed to and may be influenced by anti-sunscreen sentiments on TikTok, emphasising the critical need for awareness and effective public health strategies.

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Trends in hospitalization in patients with malignant bowel obstructions secondary to incurable gastrointestinal cancer: A retrospective cohort study using multi-state models

Tiago Ribeiro, MD 1, Julie Hallet, MD MSc 2, Calvin Diep, MD 1, Adom Bondzi-Simpson, MD, MSc 1, Wing Chan 3, Natalie Coburn, MD, MPH

1 University of Toronto; 2 Sunnybrook Health Sciences Centre; 3 ICES

Introduction: Malignant bowel obstruction (MBO) is common clinical presentation with significant life impact in patients with incurable GI cancer. We employed multi-state models to evaluate the impact of patient, cancer and treatment factors on hospital admissions, home time and death.

Methods: This was a population-based retrospective cohort study of adults with incurable gastric, pancreatic, or colorectal cancer over 2010-2019 admitted with MBO. Multi-state models were run to evaluate trends in hospitalization and the impact of defined patient, cancer and treatment factors. The four states were: MBO admission, non-MBO admission, home, and death. Transition intensities, sojourn time and total time in each state was identified in multivariable models.

Results: Of 4642 patients, we identified the following state counts: 6136 (26.4%) in MBO admission, 4409 (18.9%) in non-MBO admission, 8620 (37.0%) home, and 4120 (17.7%) who died. After developing MBO, patients with incurable GI cancer spend 2 times as long in hospital for MBO versus other reasons. Compared to patients treated with supportive care, those with surgical or procedural intervention had an over 3- and 2-times lower rate of MBO re-admission, respectively. Admission to hospital for non-MBO reason had an over 1.5 higher rate of discharge home compared to MBO admission.

Conclusion: Adults with MBO secondary to incurable GI cancer have high hospitalization rates related to recurrent MBO which improve with prior interventions.

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Enhanced Functional and Surgical Outcomes with 3D Printing in Orthopedic Oncology: A Comparative Meta-Analysis Against Conventional Techniques

Peter Joseph Mounsef, MDCM (C) 1, Anthony Bozzo, M.D., MSc, FRCSC 2, Benjamin Blackman, B.Sc 3, Ojasvi Sharma, MDCM (C) 1, Ahmed Aoude, B. Eng, M. Eng, MD, FRSC 2

1 Faculty of Medicine and Health Science, McGill University, Montreal, QC, Canada; 2 Department of Orthopedic Surgery, McGill University Health Centre, Montreal, QC, Canada; 3 School of Medicine, University of Limerick, Limerick, Ireland

Introduction: Three-dimensional printing (3DP) technology has increasingly gained attention in orthopedic oncology, where complex tumor resections and reconstructions demand high precision. 3DP enables the creation of patient-specific models and prosthesis, which can assist surgeons in preoperative planning, enhance surgical accuracy, and improve outcomes in complex oncologic cases. Despite its potential, comprehensive data on the effectiveness and applications of 3DP in orthopedic oncology are limited. This paper aims to assess whether using three-dimensional printing (3DP) compared to conventional fixation techniques results in better outcomes in orthopedic oncology, offering insights for clinicians on integrating this technology into practice and highlighting areas for further research.

Methods: A comprehensive search of Ovid MEDLINE, Embase, Scopus, and Web of Science was conducted up to November 2024. Studies comparing 3D printing to conventional methods in orthopedic oncology and reporting outcomes such as operative time, blood loss, recurrence rates, or functional scores were included. Weighted means and meta-analyses were conducted to compare these outcomes. Statistical heterogeneity was adjusted by using a random-effects model.

Results: Fifteen studies comprising 518 patients met inclusion criteria. Our primary findings were improved MSTS scores (MD: 2.17, p=0.00) and decreased blood loss (MD: 69.8 mL, p=0.00) in the 3D printing groups. No significant difference in operative time was observed between 3D printing and conventional techniques (mean difference: -12.2 minutes, p=0.32). Tumor recurrence rates did not differ significantly between groups (relative risk: 0.88, p=0.50). Subgroup analyses indicated that 3D-printed surgical guides and implants contributed to reduced blood loss, without significantly affecting OR time or recurrence rate. When examining three studies that looked at implants into the appendicular skeleton, there was a statistically significant reduction in OR time in the 3DP group (MD: -28.86, p=0.00).

Conclusion: The findings suggest that 3D printing in orthopedic oncology may enhance surgical precision by reducing intraoperative blood loss and improving post-operative function, without affecting recurrence rates. Its effect on operative time remains inconclusive. Substantial heterogeneity limits the confidence in these findings.

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Institution-level framework to estimate the impact of BMI on operative decision making inpatients undergoing colorectal surgery in Nova Scotia

Moamen Bydoun, PhD 1, Richard T. Spence, MD, PhD 2, Cameron Penny, MD 2

1 Dalhousie Medical School, Dalhousie University, Halifax, Nova Scotia; 2 Department of Surgery, Dalhousie University, Halifax, Nova Scotia

Introduction: In Canada, Nova Scotia (NS) has one of the highest obesity rates and coincidently, one of the lowest uptake of minimally invasive surgery (MIS) in colorectal patients. Excess adiposity, MIS experience level and provider preferences are factors that may hinder MIS adoption. This study presents a methodological framework that quantifies the BMI association with choice of surgical approach and unplanned conversion of colorectal surgeries in NS, benchmarked against NSQIP (National-Surgical-Quality-Improvement-Program).

Methods: This retrospective cohort study includes colectomies and proctectomies (2018-2022) from NS (n=3,373) and NSQIP (n=243,221). Categorical and continuous variables were analyzed using chi-squared-test and one-way-ANOVA, respectively. Significant univariate associations were included in multivariate logistic regression. Data analysis was performed using RStudio.

Results: When compared to NSQIP, NS had lower MIS use and higher unplanned conversion rates in colectomies and proctectomies. No significant differences in surgical approach were noted between BMI classes. However, after risk adjustment, BMI and high bleeding risk were significantly associated with conversion in NS. Both operative approaches and conversion rates varied depending on procedure and provider preferences. For instance, in procedure 44160/44205, the relative risk of conversion in NS patients with BMI≥30 was 55.9% compared to 19.6% in NSQIP. Providers with high MIS use were less likely to convert. reflecting a volume-outcome relationship. This relationship was more evident in patients with BMI≥30.

Conclusion: BMI is an independent risk factor for unplanned conversion. Adjusted conversion in NS is partly due to provider choices and lower MIS use. This study presents an opportunity for remote proctoring by higher-volume laparoscopic providers.

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Surgeon-level Variations in Breast Cancer Surgical Quality and Perceived Systemic Barriers: A Multi-Method Study in Manitoba

Maziar Fazel Darbandi, MD 1, Megan Delisle, MD MPH MSc FRCSC 1, Doris Goubran, BHSc 2, Iresha Ratnayake, MSc 3, Celine Dainhi 4, Pamela Hebbard, MD FRCSC 5, Pascal Lambert, MSc 6, Kathleen Decker, MHA PhD 7.

1 Department of Surgery, University of Manitoba; 2 Max Rady College of Medicine, University of Manitoba; 3 Department of Community Health Sciences, University of Manitoba; 4 Department of Science, University of St. Boniface; 5 Department of Surgical Oncology, CancerCare Manitoba; 6 Epidemiology and Cancer Registry, CancerCare Manitoba; 7 Paul Albrechtsen Research Institute, CancerCare Manitoba

Introduction: Variations in surgical quality influence patient outcomes. We aim to investigate variations in national breast cancer surgical quality standards between surgeons and understand surgeons’ perceptions of breast cancer surgery quality in Manitoba.

Methods: We performed a retrospective cohort study of Manitobans ≥18 years old diagnosed with invasive breast cancer or ductal carcinoma in-situ from 2018-2021. Surgical quality was measured using national breast cancer surgery standards. Univariable logistic regression was performed. We conducted 60-minute virtual semi-structured interviews guided by the Theoretical Domains Framework with surgeons who performed breast cancer surgery between 2021-2024.

Results: Twenty-five surgeons performed 4,134 surgeries, the median resection within 30 days of diagnosis was 69.1% (range=55.0-87.1%). The median margin re-excision among surgeons after breast-conserving surgery was 5.9% (range=5.9-40.0%). Patients having surgery within 30 days of diagnosis and margin re-excision were not associated with surgeon age (OR=1.0, 95% CI=0.8-1.2, p-value=1.0, OR=0.9, 95% CI=0.6-1.3, p-value=0.6 respectively), years in practice (OR=1.0, 95%

CI=1.0-1.0, p-value=0.9, OR=1.0, 95% CI=1.0-1.0, p-value=0.9, respectively), female sex (OR=0.9, 95% CI=0.6-1.4, p-value=0.7, OR=1.4, 95% CI=0.7-2.7, p-value=0.4, respectively), or Canadian medical training (OR=0.8, 95% CI=0.4-1.5, p-value=0.4, OR=0.5, 95% CI=0.2-1.21, p-value=0.1, respectively). Twelve surgeons were interviewed. Surgeons felt motivated and capable of improving surgical quality but perceive limited opportunities and barriers within the healthcare systems to do so.

Conclusion: Surgeon-level variations in breast cancer surgery quality indicators exist, which are not significantly associated with the operating surgeon. Surgeons perceived systemic factors as having a large impact on surgical quality. Completion of multivariable analyses and further understanding of the broader contextual factors are needed.

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Machine Learning-Based Prediction of Luminal Breast Cancer Subtypes Using Polarized Light Microscopy

Kseniia Tumanova, PhD candidate 1, Alex Vitkin, PhD 1, Mohammadali Khorasani, MD 2, Sharon Nofech-Mozes 1.

1 University of Toronto; 2 University of British Columbia;

Introduction: Differentiating luminal A and B breast cancer subtypes in routine histopathologic samples is challenging due to the lack of clear morphological differences, often requiring ancillary testing. Mueller matrix polarimetry offers a promising approach by analyzing polarized light interactions with complex breast tissues. This study explores the efficacy of using polarimetric parameters for luminal subtype differentiation.

Methods: We analyzed 26 polarimetric and 7 clinical parameters from 68 unstained breast core biopsies classified using the BluePrint molecular assay. These features were used to train logistic regression, linear discriminant analysis, support vector machine, random forest, and XGBoost models to distinguish luminal A from luminal B subtypes. These models, along with receiver operating characteristic curve analysis, were applied to assess diagnostic performance using area under the curve, sensitivity, and specificity.

Results: Using the top eight most prognostic polarimetric and clinical biomarkers ranked by feature importance, the best-performing random forest model achieved an accuracy of 81%, with both sensitivity and specificity at 75% on an unseen test set.

Conclusion: Mueller matrix polarimetry, combined with clinical biomarkers, shows promise in distinguishing luminal breast cancer subtypes when validated against BluePrint labels. By detecting differences in tissue morphology, this approach may enhance breast cancer prognosis and guide treatment decisions.

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The economic impact of regional communities of practice to improve quality of melanoma care

Laura Kerr, MD FRCSC 1, Carolyn Nessim, MD MSc FRCSC FACS 1, Katie Aw 1, Rebecca Lau 1, Kednapa Thavorn 2, Karine Riad 1, Boaz Wong 1, Stephanie Johnson Obaseki 1.

1 University of Ottawa; 2 OHRI

Introduction: Current best practice guidelines suggest that routine preoperative imaging may not be warranted in patients with early-stage melanoma without clinically palpable lymph nodes. A collaborative on melanoma care for the region of Eastern Ontario set guidelines supporting the restricted use of staging imaging in 2017. This study assesses the practice changes after the implementation and dissemination of the CoP guidelines for preoperative imaging in patients with <T3b melanoma who are clinically node negative.

Methods: Retrospective data from patients with biopsy-proven primary melanoma who underwent wide local excision and sentinel lymph node biopsy surgery were included. Patients were grouped into the pre- and post-guideline cohorts. Frequency, type, and positivity rate of preoperative imaging were collected and analyzed. Patient baseline demographics and tumour histological characteristics were collected for multivariable analysis. An economic analysis was performed based on the use of diagnostic work up pre- and post- guideline dissemination.

Results: Patients in the post-guideline cohort had significantly lower rates of pre-operative imaging when compared with the pre-guideline cohort (p<0.0001). On multivariable analysis, guideline dissemination was associated with lower odds of receiving preoperative imaging. A total cost savings of $9,641.50 was demonstrated, with most significant cost savings noted in reduction of CT scans of the chest, abdomen and pelvis.

Conclusion: These results demonstrated a reduction in inappropriate pre-operative imaging following CoP guideline dissemination, with favourable economic outcomes as a result. These findings support the importance of quality improvement programs such as a CoP to advance melanoma care and resource stewardship initiatives.

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Feasibility of establishing a national multidisciplinary rounds for cholangiocarcinoma or biliary tract cancer, a rare form of malignancy

Ishita Aggarwal, MD, MPH 1, Rebecca C. Auer, MD, MSc, FRCSC 2, Christine Lafontaine, MSc 3, Rachel Goodwin, MD, FRCPC 3, Cynthia Walsh, MD, FRCPC 3, Catherine Forse MD, FRCPC 3, Arif Awan, MD, FRCPC 3, Leonard Angka, PhD 3.

1 The Ottawa Hospital; 2 Ottawa Hospital Research Institute; 3 no affiliation provided

Introduction: Cholangiocarcinoma (Biliary Tract Cancer, BTC) is a rare and aggressive malignancy. The Canadian Cholangiocarcinoma Collaborative (C3) implemented Canada’s only national BTC multidisciplinary rounds (MDR) for reviewing surgical/local and systemic therapy decision making, interpreting molecular report data, sharing best practices, and raising awareness of clinical trials/emerging treatments.

Methods: C3 BTC-MDR were launched in January 2024. Uniquely, cases can be submitted by either physicians or patients. Rounds are held monthly using a secure virtual platform. An official C3 Summary Report is provided to the patient and physician(s). The rounds are accredited for Section 1 CME by the RCPSC.

Results: To date, C3 has built a community of 158 physician experts and 196 patients. 11 BTC-MDRs have been held, during which a total of 25 cases across 16 sites have been reviewed. On average, meetings have been attended by 20 experts (range 13-31). The physicians in attendance have included molecular geneticists, pathologists, radiologists, medical, radiation and surgical/hepatobiliary oncologists, and naturopaths, plus residents/fellows. Cases have spanned provinces, with submissions from Ontario (40%), BC (24%), Alberta (12%), Manitoba (8%), Quebec (4%) and Newfoundland (4%). Case patients were 64

Conclusion: National BTC-MDR have proven a critical discussion forum for cancer specialists. This model may be feasible for other rare cancers.

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Establishing Nutritional Management Guidelines For Gastric Cancer Care: A RAND/UCLA Modified-Delphi Consensus Panel

James Thistle, HBSc 1, Natalie G. Coburn, MD, FRCSC 2 , Monica Yuen, MPH, BSc 1, Cheuk See Yau, BSc 1, Ka Yan Ip, MPH 1, Andrew Faller-Saunders, MSc 1, Denise Gabrielson, RD, MSC 3, Ekaterina Kosyachkova, BScPA 4, Teresa Tiano 4, Lina Miranda 4, Elena Elimova, MD 5, Howard Lim. MD, PhD 6, Daniel Schiller, MD 7, Biniam Kidane, MD, MSc 8, Christine Brezden-Masley, MD, PhD 5, Farhana Shariff, MD 9.

1 Clinical Evaluative Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada; 2 Clinical Evaluative Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada., Department of Surgery, University of Toronto, Toronto, Ontario, Canada., Division of Surgical Oncology, Odette Cancer Centre - Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Division of Medical Oncology, St. Michael’s Hospital, Toronto, Ontario, Canada; 4 My Gut Feeling, Stomach Cancer Foundation of Canada, Toronto, Ontario, Canada; 5 Department of Medicine, University of Toronto, Ontario, Canada; 6 University of British Columbia, British Columbia, Canada; 7 University of Alberta, Edmonton, Alberta, Canada; 8 University of Manitoba, Manitoba, Canada; 9University of Manitoba, Manitoba, Canada.

Introduction: We initiated a RAND/UCLA Modified-Delphi Consensus Panel to establish nutritional management guidelines for patients with gastric cancer (GC). Guidelines addressing specific micro- and macro-nutrient testing and supplementation for the support of patients with GC, may lead to better quality of life and post-gastrectomy outcomes.

Methods: A panel of 45 interdisciplinary healthcare providers (HCPs), and 15 GC patients/advocates met virtually after initially evaluating 215 evidence-driven statements on nutritional management in GC. Appropriateness of each statement was evaluated using a 9-point Likert scale (1-3: inappropriate, 4-6: uncertain, 7-9: appropriate). Appropriateness or inappropriateness was deemed if ≥75% of respondents scored 7-9 or 1-3, respectively.

Results: After 2 rounds, a total of 303 statements were proposed for nutritional management of GC. 143 of 303 statements were rated as appropriate. The panel identified uncertainty surrounding (1) investigations of sarcopenia and bone mineral density, (2) prophylactic supplementation and (3) nutrient testing and monitoring. Longer (>5 years) follow-up periods and publicly funded support for nutritional needs were rated as appropriate. The panellists voiced that indefinite follow-up and access to cancer care providers for nutritional management was necessary. The need for a care coordinator to navigate nutrition management was identified.

Conclusion: The large number of uncertain statements reflects the lack of specific evidence and education in GC literature. This work provides a framework for nutritional care in GC while identifying the significant gaps in existing literature. Areas in which there is agreement of appropriateness will form the basis for guidelines for nutritional support for GC patients.

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Impact of Neoadjuvant Therapy on Oncologic Outcomes in Patients with Perforated Colon Cancer: A Retrospective Analysis

Irtaza Tahir, MD, MSc, Jessica D Bogach, MD, MSc, Karim Messak, MD, Cagla Eskicioglu, MD, MSc, Forough Farrokhyar, PhD

McMaster University

Introduction: Patients presenting with perforated colon cancer require emergency intervention with significant morbidity and worse survival. We aimed to assess whether neoadjuvant treatment in patients with contained perforated colon cancer was associated with improved oncologic outcomes.Patients referred to the Juravinski Cancer Center in Hamilton, Ontario, from 2008 to 2018, with diagnosed Stage I-III colon cancer who presented with contained perforation were included. Clinical details were extracted from charts, and oncologic outcomes, including 5-year overall and recurrence-free survival, were compared between those receiving neoadjuvant treatment and upfront resection.

Results: 120 patients (3.4%) presented with contained perforations. 90% of perforations were at the tumour site. 76 (63.33%) patients had upfront oncologic resection compared to percutaneous drainage (15.83%) and/or diversion (24.16%). 24 (20%) patients underwent neoadjuvant therapy and ultimately, 115 underwent oncologic resection. R0 resection rates were 75% in the neoadjuvant group versus 81.3% in the upfront resection group (p = 0.494). Recurrence occurred in 44.3% of patients. Five-year recurrence-free survival was 58%, and overall survival was 65.6%. Kaplan-Meier analysis showed no significant difference in 5-year recurrence-free or overall survival between patients receiving neoadjuvant therapy compared with upfront resection (χ² = 0.0032, p = 0.9549; χ² = 0.143551, p = 0.704776).

Conclusion: Patients with perforated colon cancers have high recurrence rates and decreased survival. While our analysis did not show significant differences between upfront resection and neoadjuvant treatment, selection bias may be impacting these outcomes. Further research is needed to optimize treatment strategies and improve outcomes.

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Depending on the nanorobots to eradicate of cancer : Prospective Study

Ibrahim Almabrouk Mohammed Ali

Faculty Of Medicine, Sabaratha University, Libya

Introduction: Nanorobots are an advanced technology recently applied in various fields, with the most significant impact in medicine, particularly surgery, They enhancing precision and reducing procedural risks.

Methods: A prospective study published in SC Biological and Pharmaceutical Sciences on (Jan 2025) involved the potentiation , Selectivity and potency of nanorobotics to find out and destroyed the cancer cells.

Results: The prospective study demonstrated promising results, confirming the efficiency, precision, and safety of nanorobots in surgical interventions, particularly minimally invasive surgeries. Additionally, they significantly reduced potential side effects, highlighting their reliability.

Conclusion: The utilization of nanorobots in surgical procedures, especially minimally invasive surgeries, marks a revolutionary advancement in precision medicine. Their application enhances accuracy, reduces complications, and improves overall surgical efficiency.

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The impact of COVID-19 on the surgical treatment of breast cancer (TICTOC): A population-based analysis.

Gary Tsun Yin Ko, MD, MSc 1; Tulin Deniz Cil, MD, MEd, FRCSC, FACS 1; Amanda Roberts, MD, MSc 2; Qing Li, MMath 3; Ning Liu, PhD 3; Toni Zhong, MD, MHS 1; Eitan Amir, MD, PhD 1; Anne Koch, MD, PhD 1; Andrea Covelli, MD, PhD 4; Vivianne Freitas, MD, MSc 1; Antoine Eskander, MD,ScM 2.

1 Princess Margaret Cancer Centre, University Health Network, 2 Odette Cancer Centre, Sunnybrook Health Sciences Centre, 3 IC/ES, 4Sinai Health System - Mount Sinai Hospital

Introduction: While studies have shown a reduction in breast cancer (BC) surgical volumes during the pandemic, few have described volume changes in different types of surgery and volume trends after the immediate pandemic remain largely unexplored. The objective of this study was to assess volumes of different types of BC surgery at a population level since the pandemic.

Methods: We identified BC surgeries between January 1, 2018 and June 25, 2022 in Ontario, Canada. Surgical volume and types of BC surgery were compared between three periods: pre-pandemic (January 2018 to March 14, 2020), immediate pandemic (March 15, 2020 to June 13, 2020), and peri-pandemic (June 14, 2020 June 25, 2022). Segmented negative binomial regression models were used to quantify the weekly surgical volume trend within each period and the change in mean volume between time periods.

Results: There were 50,440 surgeries performed among 44,226 patients. During the immediate pandemic, there was a 16.9% reduction in weekly BC surgeries (180.5 + 32.5 vs pre-pandemic: 217.1 + 43.7; p = 0.028), which returned to pre-pandemic levels in June 2021. Mastectomies represented a higher proportion of BC surgeries in the immediate and peri-pandemic periods (31.1% pre-pandemic, 36.3% immediate pandemic, & 32.4% peri-pandemic; p&lt; 0.001). During the immediate pandemic, the proportion of mastectomies with immediate reconstruction (17.0% vs. pre-pandemic: 14.7%; p=0.099) remained stable, but significantly increased in the peri-pandemic period (20.1% vs. pre-pandemic: 17.0%; p&lt;0.001).

Conclusion: During COVID-19, BC surgery volume decreased significantly, with a prolonged time to recovery with mastectomies representing a higher proportion of BC surgeries.

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Hospitalizations and emergency visits for Ontario breast cancer patients undergoing neoadjuvant chemotherapy with pembrolizumab: A population-based analysis

Gary Ko, MD 1, Tulin D. Cil, MD, MEd 2, Matthew Castelo, MD 1, Qing Li, MMath 3, Ning Liu, PhD 3, Eitan Amir, MD, PhD 4, Andrea Covelli, MD, PhD 5, Antoine Eskander, MD, ScM 6, Viviane Frietas, MD, MSc 7, C. Anne Koch, MD, PhD 8, Jenine Ramruthan, MSc 2, Emma Reel, MSW 2, Amanda Roberts, MD, MSc 9, Toni Zhong, MD, MHS 10.

1 Division of General Surgery, Department of Surgery, University of Toronto, ON, Canada; 2 Division of General Surgery, Department of Surgery, Princess Margaret Cancer Centre – University Health Network, Toronto, ON, Canada; 3 Institute for Clinical Evaluative Sciences (ICES), Toronto, ON, Canada; 4 Division of Medical Oncology, Department of Medicine, University of Toronto, ON, Canada; 5 Division of Surgical Oncology, Department of Surgery, Mount Sinai Hospital, Toronto, ON, Canada; 6 Department of Otolaryngology - Head and Neck Surgery, Michael Garron Hospital and Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada; 7 Department of Medical Imaging, University of Toronto, ON, Canada; 8 Department of Radiation Oncology, University of Toronto, ON Canada; 9 Department of Surgery, Sunnybrook Health Sciences Centre, Toronto, ON, Canada; 10 Division of Plastic Surgery, Department of Surgery, University of Toronto, Toronto, ON, Canada.

Introduction: Immunotherapy-containing neoadjuvant chemotherapy (NAC) regimens for breast cancer (BC) may be associated with immune-related adverse events and increased healthcare utilization. The objective of this study was to assess the emergency department (ED) visits and hospitalizations among BC patients undergoing NAC in Ontario.

Methods: Adjusted odds of ED visits and hospitalizations during the neoadjuvant period (diagnosis to surgery) and post-operative period (30 days from surgery) were analyzed for BC patients undergoing NAC with pembrolizumab, anti-HER2, or chemotherapy alone (CA) between April 2022-August 2023.

Results: Among 1301 BC patients (median age 52; 94.7% without comorbidities) 229 patients (17.6%) had NAC with pembrolizumab, 532 (41.0%) with anti-HER2, and 540 (41.4%) had CA. Patients with pembrolizumab were more likely to have ED visits (anti-HER2: aOR 1.79, 95% CI 1.31-2.45 & CA: aOR 1.61, 95% CI 1.18-2.21) during the neoadjuvant period, but not during the post-operative period (anti-HER2: aOR 1.30, 95% CI 0.85-1.97 & CA: aOR 1.32, 95% CI 0.87-1.99). Patients receiving pembrolizumab had higher odds of hospitalization during the neoadjuvant period (anti-HER2 aOR 2.78, 95% CI 1.92- 4.04 & CA: aOR 3.94, 95% CI 2.66 -5.83, ) and similar odds to patients undergoing anti-HER2 therapy (aOR 1.63, 95% CI 0.77- 3.43), but slightly higher than CA (aOR 2.54, 95% CI 1.13-5.72) during the post-operative period.

Conclusion: Pembrolizumab containing NAC was associated with higher odds of ED visits and hospitalizations during the neoadjuvant period, but not in the post-operative period. Further work to understand the etiology and mitigate these events is needed.

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Pre-treatment time intervals and patterns of referral in pelvic soft tissue sarcoma

Catherine Sarre, MD MSc MHA, Carol J. Swallow, MD PhD, Harini Suraweera, Wendy Johnston, Rebecca Gladdy, MD PhD, Savtaj Brar, MD.

University of Toronto

Introduction: Pelvic soft tissue sarcoma (P-STS) is rare, and patients may experience delays in diagnosis, referral and management. We investigated the nature and duration of pre-treatment delays in these patients.

Methods: We measured 5 pre-treatment time intervals (see Fig. 1) in consecutive patients with P-STS managed at a single sarcoma centre between 01/2000 and 07/2024. Comparisons between groups were by Mann-Whitney U test.

Results: 177 patients with P-STS were included (M/F=91/86, median age 56). Top 3 histologies were leiomyosarcoma, dedifferentiated liposarcoma and solitary fibrous tumor (n=38, 31 and 19). Pre-treatment biopsy was done in 146 patients (82%). In 71 cases (40%), histologic diagnosis was changed after pathology review at the sarcoma centre. Prior to referral, 64 (36%) patients underwent surgery, 10 (6%) systemic treatment and 4 (2.3%) radiation. Median interval from onset of symptoms to first medical visit was 2 weeks (IQR 0.7-7.4); from that visit to first consultation at the sarcoma centre 16.3 weeks (IQR 8-33.1); from consultation to starting treatment 6 weeks (IQR 3-9.4). Median interval from first medical visit to P-STS diagnosis was 11.1 weeks (IQR 5.3-25.5). Median total pre-treatment interval (from 1st medical visit to starting treatment) was 21.4 weeks (IQR 13.9-40.7). There were no differences based on patient sex, age, or tumor histology.

Conclusion: In patients with P-STS managed at a sarcoma centre, the most significant source of delay prior to initiation of treatment was related to diagnosis and referral, i.e. system-level factors. Greater awareness and referral prior to confirmed diagnosis could address these challenges.

Neoadjuvant Radiotherapy in Retroperitoneal Sarcoma (RPS): Data Dissemination and Practice Patterns Post STRASS
Alexandra Allard-Coutu 1; Carolyn Nessim 1; Victoria Dobson 1, Christina L. Roland 2, Sarah Corn 3, Sinsiana Dumitra 3, Carolyn Freeman 4, Dario Callegaro 5, Chandrajit P. Raut 6, Alessandro Gronchi 5.

1 Department of Surgery, The Ottawa Hospital and Research Institute, University of Ottawa, Ottawa, ON K1H 8L6, Canada; 2 Department of Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA; 3 Department of Surgical Oncology, McGill University Health Centre, Montreal, QC H4A 3J1, Canada; 4 Department of Radiation Oncology, McGill University Health Centre, Montreal, QC H4A 3J1, Canada; 5 Department of Surgery, Fondazione IRCCS Istituto Nazionale Dei Tumori, 20133 Milan, Italy; 6 Department of Surgery, Brigham and Women’s Hospital and Dana-Farber Cancer Institute, Harvard Medical School, Boston, USA.

Introduction: The phase 3 randomized STRASS (EORTC 62092) trial demonstrated no significant difference in the primary endpoint of 3-year abdominal-recurrence-free survival (HR 1.01, p=0.954) for patients with primary RPS treated with neoadjuvant radiotherapy (RT) followed by surgery compared to surgery alone. An international survey following initial presentation of the results at the American Society of Clinical Oncology (ASCO) Annual Meeting but prior to publication revealed only 20% of 80 responding clinicians adopted practice changes. This study (1) compares results of our original survey to a new one completed post publication of STRASS to assess practice patterns among international sarcoma experts and (2) explores dissemination and integration of new knowledge into clinical practice.

Methods: A 12-question survey was distributed in December 2022 to two international organizations including all specialties treating RPS (Trans-Atlantic Australasian Retroperitoneal Sarcoma Working Group, and the Canadian Society of Surgical Oncology). Clinical scenarios established the likelihood of recommending neoadjuvant RT, with a 5-point Likert-scaled response ranging from very unlikely to very likely. Low kappa correlation coefficients indicate considerable change. The data were analyzed using STATA 12 (Statacorp, College Station, TX, USA).

Results: A 139/300 clinicians responded (46.3% response rate), including surgical (70.5%), radiation (18.0%) and medical oncologists (8.6%). While 51.1% identified practice changes subsequent to the abstract, 68.1% reported changes following manuscript publication. 63.7% now offered neoadjuvant RT to select patients with RPS based on histology, while 35.3% reported rarely/never offering preoperative RT. Recommendations for neoadjuvant RT for leiomyosarcoma fell from 58.7% to 18.4% following the abstract, and to 8.9% post publication. Recommendations for neoadjuvant RT for well-differentiated liposarcoma increased from 33.9% to 60.2% following the abstract, and to 70.5% following the manuscript (Table 1). Of note, 56.3% continue to offer neoadjuvant RT to dedifferentiated liposarcoma post publication of STRASS. Clinical or institutional experience was not predictive of practices changes. total of 1391 unique BCS operations for invasive breast cancer were identified for study inclusion. 158 patients underwent at least one revisional surgery with a median time to repeat procedure of 34 days. Among surgical facilities, the average re-operation rate was 11.4% with marked variability between sites (5.2%-18.5%). Completion mastectomy was performed in 5.4% of patients and 1.5% of patients underwent more than one revisional surgical procedure. On multivariate analysis, tumor multifocality was associated with revisional surgery (OR 2.80).

Conclusion: Practice patterns for neoadjuvant RT for primary RPS changed in response to the publication of STRASS. Ongoing recommendations for neoadjuvant RT for dedifferentiated liposarcoma and/or high grade histologies highlight the necessity of a systematic approach for disseminating practice-changing data.

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Endoscopic miss rate of gastric adenocarcinoma in British Columbia

Lior Flor, MD 1, Trevor Hamilton, MD MSc FRCSC FACS 1, Michal Pillar 1, Roberto Trasolini 2

1 University of British Columbia; 2 Division of Gastroenterology, University of British Columbia

Introduction: Endoscopic miss rate of gastric adenocarcinoma (GA) is poorly described in North American populations. Previous studies report a pooled miss rate of 11.3% (4.6% - 25.8%). This study aims to evaluate the endoscopic miss rate of GA and associated factors in a North American population.

Methods: This population-based retrospective review included 354 patients diagnosed with GA in a health region. A miss was defined as an endoscopy performed within 3 years of a GA diagnosis that did not diagnose GA (excluding scopes performed within 1 month of the diagnostic scope). Data on patient demographics, endoscopic findings, surgical pathology, and survival were collected and analyzed.

Results: The overall miss rate was 7.9%. Symptoms were the indication for endoscopy in 78.6% of missed endoscopies. Biopsies at the time of endoscopy revealed gastritis (75%), intestinal metaplasia (57.1%), low-grade dysplasia (17.6%), and high-grade dysplasia (10.7%). 57.1% of missed cancers and 52.7% of non-missed cancers, went on to surgery. 50% of missed cancers were stage I, 62.5% were T1, and 62.5% were greater than or equal to 2 cm. On multivariate logistic regression, higher T stage tumors were less likely to have been missed (p&lt;0.001, 95%CI 0.24-0.71). Survival was worse in non-missed cancers versus missed cancers (OS 33.7 vs. 47.3 months, p = 0.041).

Conclusion: Endoscopic miss rate for GA in a North American population is significant. Missed scopes frequently identified premalignant pathologies. Improved overall survival in missed cancers may suggest that earlier cancers are more likely to be missed.

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Axillary Surgery after Neoadjuvant Chemotherapy: Population-Based Trends over Time

Ekaterina Kouzmina, MD 1, Amanda Roberts, MD, MPH 2, Matthew Castelo, MD 1, Nicole J Look Hong, MD, MSc 2, Julie Hallet, MD, MSc 2, Natalie Coburn, MD, MPH 2, Frances C. Wright, MD, Med 2, Lena Nguyen, MSc 3, Sonal Gandhi, MD, MS, Katarzyna Jerzak, MD, MSc 2, Andrea Eisen, MD 2

1 University of Toronto; 2 Sunnybrook Health Sciences Centre; 3 ICES;

Introduction: Sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy (NAC) has recently become the standard of care for patients with cN1 disease converted to cN0. We aimed to describe real-world population-level trends of axillary surgery de-escalation NAC over an 8-year period.

Methods: A population-based cohort study of women aged 18 years or older with cT1-3N1 breast cancer in Ontario who underwent NAC and subsequent surgery between April 2012- January 2020 was performed. Axillary surgery (SLNB, axillary lymph node dissection (ALND), SLNB followed by ALND) and trends over time were evaluated using Cochran Armitage test and grouped by procedure type and receptor subtype.

Results: Between 2012-2020 (n = 2,692), SLNB and SLNB + ALND increased by 24.1% (p &lt; 0.01) and by 2.9% (p &lt; 0.01) respectively. ALND decreased by 26.9% (p &lt; 0.01). SLNB use increased by 12.6% (p &lt; 0.01) for hormone receptors positive (HR+) cancers, 33% (p &lt; 0.01) for HER2+ cancers, and 29.6% (p &lt; 0.01) for triple negative (TN) cancers. HR+ cancers had a decrease in ALND of 18.7% (p &lt; 0.01), HER2+ cancers - of 35.6% (p &lt; 0.01), and TN cancers - of 28.4% (p &lt; 0.01). HR+ cancers had an increase in SLNB + ALND of 6.1% (p &lt; 0.01), HER2+ cancers of 2.6% (p &lt; 0.01), and TN cancers of 4% by 2017, then a decrease of 5% by 2020 (p &lt;0.01).

Conclusion: De-escalation of axillary surgery to SLNB has increased over time for appropriately selected cN1 patients post NAC.

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Compassion Fatigue in Surgical Oncologists: A Scoping Review

Mariah D. Moti, MD 1, Farhana Shariff, MDCM, MSc(HPE) 1, Catherine Sarre Lazcano, MD, MSc 2, Janice Liton, BA 3

1 University of Manitoba, Department of General Surgery; 2 University of Toronto, Department of Surgery, Division of Surgical Oncology; 3 University of Manitoba

Introduction: The practice of clinical oncology includes diverse and complex clinical, interpersonal and ethical challenges that can lead to physical and/or emotional distress, including burnout (BO), compassion fatigue (CF), secondary traumatic stress (STS) or moral distress (MDS), which potentially impacts patient care and provider well-being. Surgical oncology presents additional stressors and challenges, yet little is known about CF, STS, and MDS in this population, and the greater body of literature in oncology is heterogenous. The aim of this paper is to review current literature regarding CF, MDS, and STS in clinical oncologists, with a focus on surgical oncologists.

Methods: Searches of OVID Medline and Embase databases were performed, as well as relevant bibliographies to identify articles related to CF, STS and MDS in clinical and surgical oncologists. Descriptive analysis was completed on relevant articles to address common definitions, themes, and potential aggravating/protective factors.

Results: 619 articles were retrieved, of which 196 underwent data extraction. Of these, 48 articles were related to CF, MDS, or STS in oncologists and 5 included surgical oncologists. There was no data specific to surgical oncologists. Definitions of the terms were inconsistent across the literature. Potential contributing factors for CF/STS/MDS are related to the work environment, time pressures, and poor communication skills. In contrast, self-care, supportive colleagues/supervisors, and experience appear to be protective.

Conclusion: This study highlights a need for standardized definitions to accurately capture and explore each of these phenomena. Further research is needed to provide insight into the challenges faced by surgical oncologists and how to support them.

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Long-term outcomes following cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for peritoneal carcinomatosis of colorectal origin.

Kadhim M Taqi, MD, FRCSC 1, Lloyd Mack 1, Jay Lee, MD 1, Scott Hurton, MD MSc FRCSC 2, Cecily Stockley, MD MPH FRCSC 1, Justin Rivard, MD MSc FRCSC FACS 2, Walley Temple, MD FRCSC FACS 1, Antoine Bouchard-Fortier, MD MSc FRCSC 1

1 University of Calgary; 2 University of Manitoba

Introduction: Cytoreductive surgery (CRS) and Hyperthermic intraperitoneal chemotherapy (HIPEC) is a major treatment modality of colorectal peritoneal carcinomatosis (CPC). The aim of this study was to determine the disease-free survival (DFS) and overall survival (OS) of patients undergoing CRS-HIPEC for CPC and factors associated with long-term survival (LTS).

Methods: All consecutive patients with CPC who underwent CRS-HIPEC in a HIPEC center between 2007-2021 were included. Actual survival was calculated using Kaplan-Meier curves and true 2-year and 5-year OS and DFS were calculated. Cox proportional hazards models were used to identify factors associated with OS, DFS and LTS.

Results: There were 125 patients with CPC who underwent primary CRS-HIPEC between 2007-2021, with mean age of 54.5 years. Median follow-up was 30.6 months (5-195). Average intraoperative PCI was 11, and complete cytoreduction (CC-0) was achieved in 96.8%. Most (80.8%) received preoperative systemic chemotherapy. The median survival was 32 months (5-193). The 2-year and 5-year OS were 68% and 24.8%, respectively, while the DFS at 2-year was 28.8% and at 5-year 14.4%. Factors associated with worse OS included pre-HIPEC systemic therapy, synchronous extra-peritoneal metastasis, and PCI ≥20 (p&lt;0.05). Disease progression prior to CRS-HIPEC was associated with worse DFS (p&lt;0.05). Lower PCI, fewer complications, lower disease recurrence and longer DFS were associated with LTS (p&lt;0.05).

Conclusion: CRS and HIPEC offers improved OS in patients with CPC, however, it remains a challenging entity with high recurrence. Response to preoperative systemic therapy, presence of extra-peritoneal synchronous metastasis and peritoneal disease burden can help predict outcomes.

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Trends in hospitalization in patients with malignant bowel obstructions secondary to incurable gastrointestinal cancer: A retrospective cohort study using multi-state models

Tiago Ribeiro, MD 1, Julie Hallet, MD MSc 2, Calvin Diep, MD 1, Adom Bondzi-Simpson, MD, MSc 1, Wing Chan 3, Natalie Coburn, MD, MPH

1 University of Toronto; 2 Sunnybrook Health Sciences Centre; 3 ICES

Introduction: Malignant bowel obstruction (MBO) is common clinical presentation with significant life impact in patients with incurable GI cancer. We employed multi-state models to evaluate the impact of patient, cancer and treatment factors on hospital admissions, home time and death.

Methods: This was a population-based retrospective cohort study of adults with incurable gastric, pancreatic, or colorectal cancer over 2010-2019 admitted with MBO. Multi-state models were run to evaluate trends in hospitalization and the impact of defined patient, cancer and treatment factors. The four states were: MBO admission, non-MBO admission, home, and death. Transition intensities, sojourn time and total time in each state was identified in multivariable models.

Results: Of 4642 patients, we identified the following state counts: 6136 (26.4%) in MBO admission, 4409 (18.9%) in non-MBO admission, 8620 (37.0%) home, and 4120 (17.7%) who died. After developing MBO, patients with incurable GI cancer spend 2 times as long in hospital for MBO versus other reasons. Compared to patients treated with supportive care, those with surgical or procedural intervention had an over 3- and 2-times lower rate of MBO re-admission, respectively. Admission to hospital for non-MBO reason had an over 1.5 higher rate of discharge home compared to MBO admission.

Conclusion: Adults with MBO secondary to incurable GI cancer have high hospitalization rates related to recurrent MBO which improve with prior interventions.

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Re-excision Rates After Breast Conserving Surgery for Invasive Breast Cancer – A Provincial Perspective

Joanna Ryan, MD MEd, Lashan Peiris, MBBS, Sunita Ghosh, PhD, A. Nikoo Rajaee, MD, David Olson, MD, David M. Lesniak MD PhD

University of Alberta

Introduction: There is extensive variability in revisional surgery rates after breast conserving surgery (BCS). This variability has been demonstrated between both surgical facilities and individual surgeons. This study aims to describe the current trends of revisional surgery after BCS within Alberta and identify opportunities for quality improvement.

Methods: All patients undergoing BCS for invasive breast cancer in Alberta were eligible for inclusion. A retrospective review of the SynoptecTM database was performed for the year 2020. Surgical facility, primary and revisional surgeries, tumor biology, patient demographics, and use of strategies for intra-operative margin assessment were recorded and compared by univariate and multivariate analyses.

Results: A total of 1391 unique BCS operations for invasive breast cancer were identified for study inclusion. 158 patients underwent at least one revisional surgery with a median time to repeat procedure of 34 days. Among surgical facilities, the average re-operation rate was 11.4% with marked variability between sites (5.2%-18.5%). Completion mastectomy was performed in 5.4% of patients and 1.5% of patients underwent more than one revisional surgical procedure. On multivariate analysis, tumor multifocality was associated with revisional surgery (OR 2.80).

Conclusion: This study describes revisional surgery and completion mastectomy rates consistent with the published literature. Additionally, there is variability in revisional surgery rates for BCS among hospitals in the province of Alberta. Future work should be targeted to further characterize factors contributing to this heterogeneity and the development of educational and quality improvement initiatives to standardize the provision of high-quality surgical care for breast cancer patients across the province.

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Implementation of a multidisciplinary Enhanced Recovery After Surgery program for Cytoreductive Surgery (CRS) with Hyperthermic Intraperitoneal Chemotherapy (HIPEC)

Cecily Stockley, MD MPH FRCSC, Melina Deban, MDCM, FRCSC, Antoine Bouchard-Fortier, MD, MSc, FRCSC, Jennifer Mateshaytis, MD, MSc, Kadhim Taqi MD, FRCSC, Michael Chong, B.Sc, MD, FRCPC Anesthesiology, Gregg Nelson, MD PhD FRCSC, Lloyd Mack, MD, FRCSC, FACS

University of Calgary

Introduction: Cytoreductive Surgery with Hyperthermic Intraperitoneal Chemotherapy (CRS/HIPEC) has been associated with high morbidity and prolonged hospital stays. We designed and implemented a novel Enhanced Recovery After Surgery (ERAS) based on ERAS Society guidelines and aimed to assess its impact on clinical outcomes.

Methods: A retrospective study on patients who underwent CRS/HIPEC from January 1, 2018, to October 31, 2022, with ERAS implementation on February 1, 2022. The primary outcome was ERAS compliance, and secondary outcomes included length of stay (LOS) and post-operative complications. Ethics approval was obtained from the local Health Research Ethics Board.

Results: 80 patients underwent CRS/HIPEC: 59 in the Historical Group, and 21 in the ERAS Group, with the respective groups being similar in age (mean: 55.7 and 53.3), comorbidities (ASA class III, 60% and 52%), and Peritoneal Carcinomatosis Index (mean: 14 and 11). Comparing the historical and ERAS groups respectively showed an increase in compliance to ERAS protocols from 26.5% to 51.5% (p&lt;0.001), while the median LOS decreased from 14 days (IQR: 10.5-21.5) to 9 days (IQR: 7-11) (p&lt;0.001), with no significant difference in the major morbidity rate (13.6% vs 9.5%) or 30-day readmission rate (9.4% vs 4.8%), and no mortalities in either group. With adjustment for patient characteristics, the mean LOS decreased in the ERAS group by 6.94 days (95% CI, 3.52-10.36, p&lt;0.001).

Conclusion: Implementation of an ERAS CRS/HIPEC program is safe with no increased morbidity or mortality and associated with positive outcomes including significantly improved compliance to ERAS protocols and a decrease in LOS.

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The epidemiology, treatment and outcomes of males diagnosed with breast cancer in Ontario, 2007-2017: a population-based analysis

Georgia Nelson, MD(C) 1, Sean Bennett, MD, MSc 1, Nouf Almarzooqi, MD 2, Manisha Jogendran, MD 1, Maya Djerboua, MSc 3, Brooke E. Wilson, MD, MSc 1, Jennifer A. Flemming, MD, MSc 1, Shaila J. Merchant, MD, MSc 1

1 Queen’s University; 2 McGill University; 3 ICES - Queen's

Introduction: Breast cancer in male patients (MBC) is uncommon, and its treatment is largely extrapolated from female patients. This study aimed to describe the epidemiology, treatment, and outcomes in a contemporary cohort of MBC patients.

Methods: We performed a retrospective cohort study of males diagnosed with breast cancer between 2007-2017 using administrative data from Ontario. Descriptive statistics were reported. Trends in treatment were analyzed, and cancer-specific survival (CSS) was calculated from time of diagnosis.

Results: A total of 868 MBC patients were identified, with a mean age of 68.6. At diagnosis, 26% were stage 1, 39% stage 2, 14% stage 3, and 7% stage 4 (14% missing). In those with available cancer subtyping, 82% were ER+/PR+/HER2-, 10% were HER2+, and 3% were triple-negative. Breast surgery was performed in 78% of patients (70% mastectomy, 30% lumpectomy). Lymph node sampling was performed in only 55% of surgical patients. Frequency of lymph node sampling increased over time, up to 73% during 2015-2017 (p&lt; 0.0001). Systemic therapy within 6 months after surgery was observed in 49%, with increasing utilization over time (p&lt; 0.0001). Radiation therapy within 6 months of surgery was used in 36% with no change over time (p=0.2). Five-year CSS by stage was 96%, 88%, 79%, and 16% for stages 1-4.

Conclusion: Males with breast cancer have predominantly ER+/PR+/HER2- subtype. Mastectomy was the most commonly performed breast surgery, with increasing use of axillary staging over time. Cancer survival statistics in MBC are favourable for non-metastatic disease, but slightly inferior to those typically reported in females.

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Association of socioeconomic status and the receipt of adjuvant chemotherapy in stage III colon cancer: a population-based cohort study

Adom Bondzi-Simpson, MD, MSc 1, Julie Hallet MD, MSc 1, Ramy Behman MD PhD 2, Tiago Ribeiro, MD 1, Sheron Perera, MD 1, Aisha Lofters, MD PhD 1, Rinku Sutradhar, PhD 1, Rebecca A. Snyder, MD MPH 3, Callisia Clarke MD MS 4, Natalie G Coburn, MD MPH 1

1 University of Toronto; 2 Memorial Sloan Kettering; 3 MD Anderson; 4 Medical College of Wisconsin;

Introduction: Adjuvant chemotherapy decreases recurrence and improves overall survival. However, not all patients access care equally. We measured the association of marginalization on quality indicators in stage III colon cancer.

Methods: We conducted a population-based retrospective cohort study of adults operated for stage III colon cancer (2007- 2020). The primary exposures were SES and ethnic diversity defined by ecologic measures from census data, both captured as quintiles. Outcomes were receipt of medical oncology consultation and adjuvant therapy within 3-months of surgery. Logistic regression examined the association between each exposure and outcomes while adjusting for confounders.

Results: Of 14,511 patients, 6,539 (45.6%) received medical oncology consultation and 8,814 (61.4%) adjuvant chemotherapy within 3-months of surgery. After adjusting for age, sex, surgical approach, and comorbidities, the lowest SES quintile was associated with lower odds of medical oncology consultation (odds ratio – OR 0.84; 95% confidence interval – CI 0.75-0.93) and of adjuvant chemotherapy (OR 0.70; 95%CI 0.62-0.80), compared to the highest quintile. The highest ethnic diversity quintile was associated with lower odds of medical oncology consultation (adjusted OR 0.88; 95%CI 0.79-0.98) and adjuvant chemotherapy (adjusted OR 0.92; 95%CI 0.64-0.82), compared to the lowest diversity quintile. When extending outcomes to 6-months after surgery, these associations persisted. When restricting to patients who had a medical oncology consultation, the lowest SES quintile was associated with lower odds of adjuvant chemotherapy (OR 0.75; 95%CI 0.61-0.93) but there was no association for ethnic diversity.

Conclusion: Within a universal healthcare system, lower SES and higher ethnic diversity were associated with lower odds of medical oncology consultation and adjuvant chemotherapy after resection for stage III colon cancer. These findings outline inequity in access to and receipt of care that may translate into differences in oncologic outcomes and suggests areas where physicians may intervene to improve the care of vulnerable patient groups.

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How Reliable is YouTube Content Targeting Arabic-Speaking Breast Cancer Patients Regarding Post-Mastectomy Reconstruction?

Haifa Alotaibi, MD 1, Ari N. Meguerditchian, MD, MSc, FRCS, FACS 1, Marya A. Alsuhaibani, MD 1, Abeer Alsulaimani, MD 2, Eric Belzile 3, Nina Morena 1

1 McGill University; 2 Taif University; 3 St. Mary’s Research Centre

Introduction: Social media platforms, notably YouTube (YT), have transformed how breast cancer (BC) patients access information. This study evaluates the quality of YT videos addressing post-mastectomy reconstruction (PMR) for Arabic speaking women (ASW), a digitally connected segment facing challenges in accessing medical information in Arabic language (AL).

Methods: In July 2023, a YT search using "post mastectomy reconstruction" in AL identified 109 videos (average length: 7 mins.). Video metrics, including upload date, length, views, and poster identity, were collected. Physician-reviewers (PR) assessed video understandability and actionability using the Patient Education Materials Assessment Tool for audiovisual materials (PEMAT A/V) and quality with the DISCERN tool. Sponsorship, audience, and thematic analysis and cluster analysis were performed.

Results: 67% of videos had sponsorship (45% corporate); 92% were information-based; 82% targeted the general population over BC patients; 93.6% were in AL. Mean PEMAT scores were 61.3% (understandability) and 20% (actionability), and the mean DISCERN score was 2.6/5. Only 21% of videos featured women. Predominant themes included awareness (82.6%) and body image (68.8%), while less prevalent topics were sexuality and fertility (4.6%). Cluster analysis revealed high-quality videos had better understandability (74%), actionability (40.5%), and a higher likelihood of PR recommendation (90.5%).

Conclusion: In summary, YT content on PMR for ASW is generally understandable but lacks actionability and exhibits moderate quality. Videos are heavily sponsored and may not adequately represent patients' perspectives. Improving YT content, especially in AL, is vital for BC patients exploring PMR, and provide guidance for content creators in enhancing digital resources for this connected demographic.

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Reduced Resections Margins for Head and Neck Cutaneous Melanoma

Uriel Clemente-Gutierrez, MD, Kumar Alok Pathak, Mahmoud Seif-Elnasr

Department of Head and Neck Oncology, Cancer Care Manitoba, University of Manitoba, Winnipeg, MB, Canada

Introduction: There are no guidelines regarding the margin of excision recommended for head and neck cutaneous melanoma (HNCM). The objective of this study was to examine the impact of different margins of excision in local, regional and distant recurrence as well as disease specific survival in patients with HNCM.

Methods: Population-based study of patients with HNCM. Margins of excision were classified as reduced versus recommended as per the National Comprehensive Cancer Network guidelines. Clinical and pathological variables were evaluated.

Results: A total of 483 patients were included. Reduced margins were observed in 377 patients (78%), the rest of them had a margin as recommended by the NCCN guidelines. The mean follow-up time for all patients was 95.6 months (range 0-461.7 months). Local recurrences were observed in 27 (5.6%) of the cohort and melanoma related deaths were observed in 80 (16.6%) patients. Local recurrence free survival (LRFS) was not different with 435.4±11.5 months for the recommended margins of excision group vs 396.7±6.9 months for the reduced margins group (p=0.549). Overall recurrence free survival (RFS) was similar amongst groups with 299.5±11.5 months in the reduced margins of excision group vs 361.4±20.6 months in the other group (p=0.08). Disease specific survival (DSS) was similar between the 2 groups (p=0.325). Cox’s proportional hazard model showed Breslow’s thickness to be the single most important prognostic factor for DSS, RFS and LRSFS (HR 1.15 p&lt;0.001 , HR 1.24 p&lt;0.001 and HR 1.18 p&lt;0.001 respectively); while margins of excision did not show statistical difference for DSS, RFS or LRFS.

Conclusion: Margins of excision can be safely reduced in HNCM near vital structures without affecting local recurrence free survival or disease specific survival.

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Feasibility of a Hyperthermic Intraperitoneal Chemotherapy (HIPEC) Program for Gastrointestinal and Gynecological Cancer Care in Newfoundland and Labrador

Kala Hickey, MD., M.Sc. 1, Joannie Neveu, MD., FRCSC 2, Stephanie Gill, MD., M.Sc 3, Zoe Breen 4, Kaitlyn Harding, MD 1, Hannah Yaremko 4, Patti Power, MD., FRCSC 2, Alex Mathieson, MD., MPH., FRSCS 1, David Pace, MD., FRSCS 1

1 Department of General Surgery, Faculty of Medicine, Memorial University; 2 Department of Gynecology Oncology, Faculty of Medicine, Memorial University; 3 Department of Obstetrics and Gynecology, Faculty of Medicine, Memorial University; 4 Faculty of Medicine, Memorial University

Introduction: Peritoneal carcinomatosis is a common presentation found in advanced staged gastrointestinal and gynecological cancers. Combined cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) is associated with significant survival benefit for select patients in this population. Currently, CRS/HIPEC is not provided in Newfoundland and Labrador (NL). The Canadian HIPEC Collaborative Group recommends centres complete a minimum of one case monthly to maintain competency and achieve good outcomes. Thus, we aimed to demonstrate that an appropriate number of patients in NL require this therapy annually to support the feasibility for implementation of a CRS/HIPEC program.

Methods: A retrospective chart review of the NL Cancer Care Registry identified patients with stage IV colorectal, appendiceal or gastric cancer and stage III to IV epithelial ovarian cancer or fallopian tube carcinoma over a one-year period (Jan 1, 2020 – Jan 1, 2021) to identify the number of patients meeting criteria for CRS/HIPEC or those referred out of province to receive the treatment. Results are presented as proportions and percentages.

Results: Thirty-one patients were eligible to receive CRS/HIPEC during the study period (11 gastrointestinal, 20 gynecological). Of the gastrointestinal patients, only 45% were referred out of province for the procedure. Gynecological patients underwent CRS and systemic +/- intraperitoneal chemotherapy in NL.

Conclusion: Allowing patients to receive this standard of care treatment near home reduces financial, social, and emotional stressors. These results confirm a sufficient patient volume to safely support a CRS/HIPEC program in NL. Implementation of this program will require multidisciplinary collaboration, specialized training and equipment and protocol development.

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Real-World Clinical Outcomes of Total Neoadjuvant Therapy for Locally Advanced Rectal Cancer – A Retrospective Analysis

Dhruvin Hirpara, MD MSc FRCSC 1, Peter K Stotland, MD MSc FRCSC 2, Christina Kim MD 1, William Chu MD 3, Joanne Yu MD 2, Kathyrn Towns MD 2, Usmaan Hameed MD 2, Stan Feinberg MD

1 University of Toronto, Department of Surgery; 2 North York General Hospital; 3 Sunnybrook Hospital

Introduction: The objective of this study is to demonstrate the clinical outcomes of patients undergoing total neoadjuvant therapy (TNT) at a high-volume center providing multi-disciplinary rectal cancer care.

Methods: Retrospective cohort study of adult patients with LARC (clinical stage II or III) treated with consolidation or induction TNT between 2018-2023. Clinical outcomes including rates of clinical complete response (cCR), organ preservation, local and distant recurrence, and salvage surgery were reviewed.

Results: A total of 63 patients underwent TNT in the study period. A majority of patients had mid-low (89%), cT3/4 node-positive disease (81%). 95% of patients were treated with consolidation TNT, including long-course chemoradiation followed by FOLFOX (n=42), CAPEOX (n=15), or capecitabine (n=3). 42

Conclusion: This retrospective cohort study supports the short-term safety and feasibility of TNT for LARC. Long term follow-up and prospective validation is to follow.

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Addressing Global Inequities in Breast Cancer Genetic Testing, Counselling, and Management Among Breast Cancer Patients in Nigeria - A Healthcare Provider Educational Program

Colleen Kerrigan, MD 1; Tulin Cil, MD, MEd, FRCSC, FACS 2; Funmilola Wuraola, MBBS, FWACS 3; Jenine Ramruthan, MSc 2; Emma Reel, MSW 2; Andrea Covelli, MD, PhD, FRCSC 4; Anna Dare, MBChB, PhD, FRCSC 1; Jeanna McCuaig, PhD, MSc, CGC, CCGC 5; Larissa Peck, MSc, CGC 2; Emily Thain, MSc, CGC 2; Janet Papadakos, PhD, MEd 2; Danielle Rodin, MD, MPH, FRCPC 2; Michelle Jacobson, MD, MHSc, FRCSC 6; Olusegun Isaac Alatise, MBChB,MSc,FWACS 3.

1 University of Toronto, 2 Princess Margaret Cancer Centre, 3 Obafemi Awolowo University Teaching Hospital Complex, 4 Sinai Health - Mount Sinai Hospital, 5 University of Toronto, Molecular Genetics, 6 Women's College Hospital, Obstetrics and Gynaecology.

Introduction: Breast cancer (BC) is a significant health challenge in Nigeria, characterized by early onset, late-stage diagnosis, and prevalent triple-negative tumors. While North America offers widespread genetic testing (GT) and counselling for BC risk and management, our recent data in Nigeria show that GT access and knowledge is limited. This study aims to develop and evaluate a hybrid educational training curriculum for Nigerian healthcare providers (HCPs).

Methods: From June to September 2023 an international oncology team developed a 4-module curriculum on hereditary BC genetics. Twenty-five HCPs completed the online curriculum, followed by in-person training in Nigeria. Pre and post knowledge scores were assessed using 10 standardized questions.

Results: Participants demonstrated significant knowledge improvement across all modules. Module 1 had marked improvement in interpreting BC incidence in Sub-Saharan Africa and disparities in survival. Module 2 showed knowledge enhancement in understanding implications of BRCA1/2 mutations, risk of secondary BC, and GT outcomes (p = 0.0048, p = 0.02, p = 0.0175). Module 3 showed increased understanding in communicating variant of uncertain significance test results (p = 0.0013). Module 4 had considerable knowledge improvement with a 30.86-fold higher likelihood of identifying the tumor subtype of a BRCA1 carrier and an 11.56-fold higher likelihood of knowing the appropriate age for high-risk breast screening in women with a BRCA mutation (p = 0.0011, p = 0.0003, respectively).

Conclusion: Our study demonstrates the hybrid training model effectively improved knowledge of hereditary BC genetics among Nigerian HCPs. This collaboration underlines the importance of accessible education for equitable BC care globally.

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The impact of COVID-19 on the surgical treatment of breast cancer (TICTOC): A population-based analysis.

Gary Tsun Yin Ko, MD, MSc 1; Tulin Deniz Cil, MD, MEd, FRCSC, FACS 1; Amanda Roberts, MD, MSc 2; Qing Li, MMath 3; Ning Liu, PhD 3; Toni Zhong, MD, MHS 1; Eitan Amir, MD, PhD 1; Anne Koch, MD, PhD 1; Andrea Covelli, MD, PhD 4; Vivianne Freitas, MD, MSc 1; Antoine Eskander, MD,ScM 2.

1 Princess Margaret Cancer Centre, University Health Network, 2 Odette Cancer Centre, Sunnybrook Health Sciences Centre, 3 IC/ES, 4Sinai Health System - Mount Sinai Hospital

Introduction: While studies have shown a reduction in breast cancer (BC) surgical volumes during the pandemic, few have described volume changes in different types of surgery and volume trends after the immediate pandemic remain largely unexplored. The objective of this study was to assess volumes of different types of BC surgery at a population level since the pandemic.

Methods: We identified BC surgeries between January 1, 2018 and June 25, 2022 in Ontario, Canada. Surgical volume and types of BC surgery were compared between three periods: pre-pandemic (January 2018 to March 14, 2020), immediate pandemic (March 15, 2020 to June 13, 2020), and peri-pandemic (June 14, 2020 June 25, 2022). Segmented negative binomial regression models were used to quantify the weekly surgical volume trend within each period and the change in mean volume between time periods.

Results: There were 50,440 surgeries performed among 44,226 patients. During the immediate pandemic, there was a 16.9% reduction in weekly BC surgeries (180.5 + 32.5 vs pre-pandemic: 217.1 + 43.7; p = 0.028), which returned to pre-pandemic levels in June 2021. Mastectomies represented a higher proportion of BC surgeries in the immediate and peri-pandemic periods (31.1% pre-pandemic, 36.3% immediate pandemic, & 32.4% peri-pandemic; p&lt; 0.001). During the immediate pandemic, the proportion of mastectomies with immediate reconstruction (17.0% vs. pre-pandemic: 14.7%; p=0.099) remained stable, but significantly increased in the peri-pandemic period (20.1% vs. pre-pandemic: 17.0%; p&lt;0.001).

Conclusion: During COVID-19, BC surgery volume decreased significantly, with a prolonged time to recovery with mastectomies representing a higher proportion of BC surgeries.

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Surgeon perspectives on the approach to breast surgical oncology in Northern Province, Sri Lanka: A qualitative analysis (SPABSO)

Gayathri Naganathan, MD MSc 1; Andrea Covelli, MD PhD 2; Chrishanthi Rajasooriyar, MBBS 3; Sreekanthan Gobishankar, MBBS 3; Mithusha Ganesalingam 4; Mayurisaa Saseetharan, HBSc 5; Anna Dare, MBChB PhD 6.

1 Department of Surgery, University of Toronto, 2 Mount Sinai Hospital and Department of Surgery, University of Toronto, 3 Jaffna Teaching Hospital, 4 University of Waterloo, 5 Ontario Tech University, 6 St. Michael's Hospital and Department of Surgery.

Introduction: Breast cancer is the leading cancer diagnosis in women in Sri Lanka. Cancer care delivery within the public healthcare system in Northern Province (NP) has important limitations. This qualitative study examined NP surgeons’ experiences in providing breast cancer surgical care, identifying key factors in surgeon decision-making.

Methods: Surgeons who provide breast cancer surgical care in NP were recruited using purposive sampling. Individual semi-structured interviews were conducted via video conferencing. Transcripts were anonymized and coded using NVivo software using Thematic Analysis.

Results: Fifteen surgeons were interviewed. Major themes emerged as follows: “resource limitations” included low finances, brain-drain of personnel, and availability of infrastructure like timely imaging and histopathology; “training gaps” included low exposure to breast onco-plastics; “patient factors” included late presentation, Ayurvedic medicine use, financial strain, and low interest in cosmesis; “systemic factors” included the economic crisis and stakeholder buy-in.

Conclusion: Breast surgical decision-making in LMICs is multifactorial. While recent research from the region demonstrates an uptrend in breast conserving surgery (BCS), NP surgeons reported low patient interest for BCS. This study identified important barriers to BCS adoption in Northern Province. Further studies probing patient, stakeholder, and system factors are needed to understand whether BCS can be better adopted in Northern Province, Sri Lanka.

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Sacral Periosteal Elevation as Alternative to Sacrectomy for Advanced Rectal Cancers with Posterior Extension: Short Term Outcomes

Erika Schmitz, BSc, MD, FRCSC 1; Jason Park, BSc, MD, MEd, FRCSC 1; Raphaele Charest-Morin 2; Andrew McFadden 1; Nicolas Dea 2; Elizaveta Vasilyeva 1

1 Department of Surgery, Vancouver General Hospital, 2 Combined Neurosurgical and Orthopaedic Spine Program, Vancouver General Hospital

Introduction: En-bloc sacrectomy for resection of rectal cancers with posterior extension are associated with high morbidity. Sacral periosteal elevation (SPE) is a newly described variation on sacrectomy involving sacral cortex osteotomy and subperiosteal dissection, while preserving bone and uninvolved nerve roots. SPE allows for extending dissections to higher spinal levels while reducing morbidity, but outcome data of rectal cancers are limited. We reviewed our single institution experience with SPE in rectal cancer patients

Methods: Patients who underwent SPE for primary and recurrent locally advanced rectal adenocarcinoma with posterior extension abutting the sacrum were reviewed from 2021-2024. Negative pathologic margin (R0 resection) was the primary outcome. Secondary outcomes included intra-operative blood loss, perioperative complications, and survival.

Results: Seven patients (mean age 58) underwent SPE for primary rectal adenocarcinoma (n=1) and locally recurrent disease (n=6). Two patients underwent S5 sacrectomy after SPE (SSPE). Periosteal elevation levels included S2 (n=1), S3 (n=1), S4 (n=4) and S5 (n=1). 5/5 SPE patients and 1/2 SSPE patients had R0 resections. SPE Mean blood loss was 3.5 L (SD 2.8), and 2.7 L (SD 2.5) in SSPE. There were no deaths &lt;90 days. Two patients had minor post-operative complications (Grade 1), and five had major post-operative complications (Grade 3b) including flap dehiscence (n=3), enterocutaneous fistula and pelvic abscess. One patient had local recurrence (54 days), while three patients had distant recurrences (mean 275 days, SD 103).

Conclusion: SPE as an alternative or adjunct to sacrectomy is feasible and associated with a high R0 resection rate in well selected rectal cancer patients.

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PROgress Tracker Breast Cancer Registry: Feasibility of a Longitudinal Patient Group-Led, National Patient-Reported Outcomes (PRO) Registry to Inform Health Care Policy from the Lived Experience Over Time

Nathan Zondervan, M.D. 1; Omar. F. Khan EMBA, MD FRCPC 2; Doris Howell, RN, PhD, Emerita/Emeritus Scientist 3; Shaniah Leduc, RN (ret.), Board Chair 4; Kimberly Carson CEO 4; Amanda Gibson, BSc 5.

1 General Surgery, Department of Surgery, Cumming School of Medicine, University of Calgary, 2 Clinical Assistant Professor, Division of Medical Oncology, Department of Oncology, Cumming School of Medicine, University of Calgary, 3 Princess Margaret Cancer Research Institute, 4 Breast Cancer Canada, 5 University of Calgary, POET Program.

Introduction: PROgress Tracker Breast Cancer Registry is the first national longitudinal, non-interventional patient-reported outcome measure (PROMs) registry, using a novel, peer-to-peer engagement and retention model directed by Breast Cancer Canada and managed by the University of Calgary’s POET Program. We aim to demonstrate the feasibility and potential of this registry in centering patient voice and lived experience to inform breast cancer surgical management.

Methods: PROgress Tracker launched in October 2023 with a 10-year enrollment goal of 50,000 Canadians with Stage 0-IV breast cancer. Participants complete PROMs via a dynamic digital platform every three months for up to 10 years, assessing quality of life, self-efficacy, symptoms, adverse treatment effects and overall global functioning.

Results: Baseline demographic, clinical, treatment, PROMs and BREAST-Q surgical modules were collected from 190 geographically inclusive Canadian participants, with an average response rate of 90%. 53% received BCS, 26% mastectomy; 16% received oncologic + oncoplastic surgery. Median BREAST-Q scores (standardized scale 0-100) were reported as: ‘Physical Wellbeing – Chest’ (64), ‘Breast Sensation’ (59) and ‘Breast Satisfaction’ (43). 24% of participants reported arm swelling at least some of the time. Oncoplastic surgery recipients reported high satisfaction scores for abdomen and navel post-reconstruction, but low satisfaction with nipple reconstruction.

Conclusion: The diverse lived experience & wellbeing post-surgical management is integral to initiate patient-centered change. The high initial response rate indicates gathering surgical data of this scope is feasible, with broad national participation from the breast cancer patient community. PROgress Tracker demonstrates growing capacity to accrue real-time data, informing best practice and identifying additional required supports.

Awareness of Risk Reducing Strategies amongst High Risk Women referred for Breast Cancer Risk Assessment

Basmah Alhassan, MBBS MSc 1, Stephanie M. Wong, MD MPH 2, Marianne Bou Rjeily MD(c) 3, Victor Villareal-Corpuz RN BSc 4, Ipshita Prakash MD MSc 5, Mark Basik MD 6, Jean Francois Boileau MD MSc 7, Michael Pollak MD 8, William D. Foulkes MBBS PhD 9

1 McGill University, Montreal, Canada, King Saud University, Riyadh, Saudi Arabia, 2 Department of Surgery, McGill University Medical School, Montreal, QC, Canada, Stroll Cancer Prevention Centre, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Canada, Department of Oncology, McGill University Medical School, Montreal, QC, Canada, 3 Department of Surgery, McGill University Medical School, Montreal, QC, Canada, 4 Jewish General Hospital Stroll Cancer Prevention Centre, Montreal, QC, Canada, 5 Department of Surgery, McGill University Medical School, Montreal, QC, Canada, Stroll Cancer Prevention Centre, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Canada, Department of Oncology, McGill University Medical School, Montreal, QC, Canada, 6 Department of Surgery, McGill University Medical School, Montreal, QC, Canada, Department of Oncology, McGill University Medical School, Montreal, QC, Canada, 7 Department of Surgery, McGill University Medical School, Montreal, QC, Canada, 8 Stroll Cancer Prevention Centre, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Canada,Department of Oncology, McGill University Medical School, Montreal, QC, Canada, 9 Jewish General Hospital Stroll Cancer Prevention Centre, Montreal, QC, Canada, Department of Oncology, McGill University Medical School, Montreal, QC, Canada, Department of Human Genetics, McGill University Medical School, Montreal, QC, Canada

Introduction: Primary prevention of breast cancer in women at elevated risk includes several strategies such as endocrine prevention and risk-reducing mastectomy. The objective of this study was to evaluate awareness of different preventive strategies across high-risk subgroups.

Methods: Women referred for high risk evaluation at our institution between 2020-2022 completed an initial risk assessment questionnaire that included questions around perceived lifetime risk and consideration of preventive strategies. Wilcoxon Rank Sum and Chi-squared tests were used to compare differences across different high risk subgroups.

Results: Overall, 320 women with a median age of 44 years (IQR, 35-53 years) were referred for high risk evaluation; 120 (37.5%) germline pathogenic variant carriers (GPV), 42 (13.4%) with high-risk lesions (HRL) on breast biopsy, and 158 (49.4%) with strong family history (FH; median Tyrer-Cuzick score 27.7, IQR, 21.9-33.5). Patients from different subgroups reported similarly high levels of perceived lifetime risk (p=0.26) and concern around developing breast cancer (p=0.33). Prior to their risk-assessment, most high risk women reported that they had considered increased screening and surveillance (84.0%) and lifestyle strategies to lower risk (79.6%), while fewer patients had considered risk-reducing surgery (39.3%) or endocrine prevention (27.0%). Risk-reducing mastectomy was most considered by GPV carriers (58.9%) relative to those with HRL (32.4%) or strong FH (25.5%, p&lt;0.001). Based on current guidelines, 123 (38.4%) patients presenting for risk assessment were deemed eligible for endocrine prevention, including 85.7% with HRL and 38.6% with strong FH. Consideration of endocrine prevention prior to the first clinic visit was highest in patients with HRL and significantly lower in those with strong FH (43.2% HRL vs. 32.1% GPV vs. 18.9% FH, p=0.004).

Conclusion: Endocrine prevention is the least considered option for prevention of breast cancer in high risk women, despite eligibility in a significant proportion of those presenting with HRL or strong FH. Further research that focuses on improving awareness around endocrine prevention options and systematically evaluating candidacy is warranted.

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Radical chest wall resection and hyperfractionated accelerated radiotherapy (HART) for radiation-associated angiosarcoma of the breast: 15 years of safe and effective treatment
Alexandra Allard-Coutu, Hon BSc, MDCM, MScClin, FRCSC, University of Ottawa, Barbara Heller, Hon BSc, MD, FRSCS, McMaster University

Introduction: Radiation-associated angiosarcomas (RAS) of the breast are rare vascular tumors arising in a previous radiation field for primary breast cancer. A wide range of treatment strategies exist, and while resection remains the definitive treatment, RAS are associated with a high probability of local recurrence and poor overall prognosis. The sarcoma group at the Juravinski Cancer Centre (JCC) previously reported a case series of nine patients treated with radical resection and adjuvant hyperfractionated accelerated radiotherapy (HART). Since 2015, this has become the standard of care at McMaster University, and updated outcomes are reported for a series which now includes 14 patients treated with radical resection and adjuvant HART.

Methods: The JCC pathologic database was reviewed between the year 2006-2022 for patients with RAS. Patients who received radical surgery and immediate HART were eligible. A soft tissue sarcoma approach, rather than a mastectomy approach, was used in the surgical resection, with definitive chest wall soft tissue resection down to the level of the pectoralis muscle with en bloc simple mastectomy, including resection of the previously radiated skin below the clavicle to 2cm inferior to the inframammary crease. Definitive immediate soft tissue coverage was achieved with massive local advancement flaps. Radiotherapy was then delivered to 4500 cGy in 45 fractions three times daily using parallel opposed photon beams and electron patching, or volumetric modulated arc therapy. Primary outcome was recurrence-free survival in months, and records were reviewed for descriptive reports of toxicity. Results were compared to other institutions? experiences.

Results: In our cohort of 14 patients, the recurrence rate was 14.3% (n=2), with a median time to recurrence of 36 months. The overall survival was 77.8% over a median follow-up of 36.7 months (range 3-100 months). One of fourteen patients developed LR and metastasis, four died of other causes, one developed LR and remains disease free after re-resection, and eight are alive with no recurrent disease. Median follow up for patients alive with NED was 25 months (n=9). There were ten reports of mild skin toxicity during treatment. One patient developed chronic wound healing complications which eventually resolved, and one patient developed asymptomatic radiation osteitis of a rib.

Conclusion: Our institutional experience suggests that large normal tissue volume reirradiation with hyperfractionated accelerated radiation therapy is safe and results in improved local recurrence rates when compared to series of patients treated without adjuvant radiation.

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The role of anastomotic leak as a potential high-risk criteria in Stage II colon cancer

Ramy Behman, MD PhD 1, Julie Hallet, MD MSc 1, Natalie Coburn, MD MPH 1, Shady Ashamalla, MD MSc 1, Sheron Perera 1, Alyson Mahar, PhD 2, Irene Jeong, MSc 3

1 University of Toronto, 2 University of Manitoba, 3 Institute for Clinical Evaluative Sciences

Introduction: Anastomotic leak (AL) is common following colorectal cancer (CRC) resection. Previous studies have suggested an association between AL and disease recurrence, but results have been mixed. We examined the impact of AL after CRC resection on disease-free and overall-survival (DFS; OS) and compared AL to established high-risk criteria for which adjuvant chemotherapy is indicated in CRC.

Methods: This is a population-based retrospective cohort study of adults with stage I-III CRC undergoing primary resection (2007-2020). Time-to-event analyses compared DFS (accounting for the competing risk of death) and OS between patients with AL and those without. Fine-Gray and Cox models examined the adjusted association between AL and DFS and OS, respectively, with subgroup analyses by disease site (colon/rectum) and stage. Patients were further stratified by presence of established high risk clinical criteria (obstruction and/or perforation) and/or AL to evaluate the association of AL with outcomes, relative to other high-risk criteria.

Results: Of 57,407 patients included (39,907 colon and 17,500 rectum cancers), AL occurred in 5.9%. Median follow-up was 5.2 (IQR: 2.6-8.8) years. After adjustment, AL was associated with significantly lower DFS for colon (sub-hazard ratio, sHR 1.2, 95%CI 1.1-1.3) but not rectal cancer (sHR 1.0, 95%CI 0.9-1.1). The difference in DFS with was greatest among for Stage II colon cancer, with 3-year DFS of 63.5% (95%CI 61.8%-65.1%) with AL vs 71.4% (95%CI 71.0%-71.8%) without AL (p=0.03). AL was associated with lower OS in both colon (HR 1.4, 95%CI 1.3-1.5 and rectal cancer (HR 1.2, 95%CI 1.1-1.3). Tests of the interaction between AL and chemotherapy were not significant for neither DFS nor OS, suggesting that the impact of AL on outcomes was not mediated by its association with receipt of chemotherapy.

Conclusion: AL is independently associated with increased risk of cancer recurrence for patients with colon cancer, but not for those with rectal cancer, and with lower OS for both colon and rectal cancers. The association between AL and DFS is comparable to that of other established high-risk criteria for which adjuvant chemotherapy is indicated. The role of adjuvant chemotherapy for patients with AL after CRC resection warrants further investigation in efforts to improve outcomes.

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Care trajectory, informational needs and challenges of patients with neuroendocrine tumors: a mixed methods study
Florence Bénard1, Sandrine Huez2, Frédéric Mercier1,3, Marie-Pascale Pomey2, 3, 4

1. Surgical Oncology, Department of Surgery, Centre Hospitalier de l’Université de Montréal (CHUM), 1051 Sanguinet Street, Montreal, QC, H2X 3E4, Canada., 2. Centre d'Excellence pour le Partenariat avec les Patients et le Public, 900 Saint-Denis Street, Montréal, Québec, H2X 0A9, Canada., 3. Centre de recherche du Centre hospitalier de l'Université de Montréal (CRCHUM), 900 Saint-Denis Street, Montréal, Québec, H2X 0A9, Canada., 4. School of Public Health, Université de Montréal, 7101 Parc Avenue, Montréal, Québec, H3N 1X9, Canada.

Introduction: Patients with neuroendocrine tumors (NETs) encounter different challenges, including delayed diagnosis and difficulty finding high-quality NET-specific information. The objective was to document NET patients’ care trajectory and explore their informational needs. The study also aimed to report challenges patients faced throughout the course of their disease, more specifically when trying to obtain information, and identify patient-based solutions.

Method: Thirteen NET patients were recruited and completed a questionnaire to collect sociodemographic and disease-related data. Semi-structured interviews were conducted with each patient alone or with their spouse. Interviews were transcribed verbatim and analysis was conducted using principles of grounded theory. Thirteen patients and four spouses were interviewed. A mean of 26.6 months separated the start of symptoms and the moment of diagnosis. On average, an additional 12.8 months elapsed before referral to a specialized center. 76.5% of patients felt well informed, but only 47.1% believed available information was reliable. Facilitating factors included their relationship with NET specialists, as well as having relatives working in healthcare and a multidisciplinary team, including nurse navigators. Significant challenges included discordances between different sources of information, as well as having limited understanding of medical terms.

In conclusion, there is a need to develop high-quality, vulgarized, accessible sources of information for NET patients. Moreover, rapid referral to NET-specialized centers with access to a multidisciplinary team could ease patients’ care trajectory and facilitate information provision.

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Robotic-assisted surgery in general surgery and sub-specialty training: understanding the landscape and perspectives of Canadian program directors

Anna Dare, MBChB PhD 1, Paul Karanicolas, MD PhD 1, Hala Muaddi, MD PhD 1, Richard Walker, MD 1, Simon Laplante 1, Rachel Roke2

1 University of Toronto, 2 Sunnybrook Health Sciences Centre

Introduction: Adoption of robotic-assisted surgery (RAS) is increasing globally, including in general surgery and sub-specialty disciplines. Uptake of the technology in Canada has been slower, and it?s place in Canadian surgical training is debated. The objective of this work was to determine current exposure to RAS during Canadian general surgery and sub-specialty training, and to understand the perspectives of Canadian program directors (PDs) on the integration of RAS in their surgical training programs and curricula.

Methods: A cross-sectional, email-based, national survey of all Canadian general surgery residency and fellowship PDs was conducted in April 2022.

Results: In total, 24/83 PDs responded to the survey: 11/18 (61.1%) were general surgery residency PDs and 13/66 (19.7%) were Fellowship PDs. 91.7% (n=22/24) of respondents reported their trainees have access to a robotic surgical system, however, only 36.3% stated that this is used by trainees in a clinical setting. Only 16.7% reported having a formal RAS curriculum. Most PDs believed that RAS should be part of surgical training in Canada at the fellowship level (72.7%, n=16). Fewer thought it should be part of residency training (36.3%, n=8). A majority (59%) felt that RAS training would be relevant to the practice setting where their graduates will work.

Conclusion: Despite the presence of RAS platforms at most academic centres in Canada, few trainees have hands-on exposure. A gap exists between current RAS training and its anticipated relevance to trainees upon graduation. Focused discussion on the introduction and place of RAS within Canadian surgical training is warranted, considering educational, clinical and health system needs.

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Medial location of the primary tumor within the breast: a novel association with local recurrence after skin-sparing mastectomy with immediate reconstruction.
Michael Guo, MD 1, Noelle Davis, MD, FRCSC 1, Sita Ollek, MD FRCSC 2, Leo Chen, MSc 1, Caroline Speers, BA 3, Trevor Hamilton, MD FRCSC 1, Alan Nichol, MD CCFP 3, Caroline Lorisch, MD FRCSC 3, Noelle Davis, MD FRCSC1

1 University of British Columbia, 2 Kelowna General Hospital, 3 BC Cancer

Introduction: Skin-sparing mastectomy (SSM) with immediate breast reconstruction (IBR) is oncologically safe and provides superior cosmetic and psychological outcomes in breast cancer. Medial location of the primary tumor has been suggested to be an independent risk factor for local recurrence (LR) and poor survival. This study aims to elucidate risk factors, including tumor location, for LR in patients undergoing SSM with IBR.

Methods: Patients who underwent treatment with SSM and IBR between 1989-2012 were identified from the BC Cancer Breast Cancer Outcomes Unit database. Univariate and multivariate analyses were used to evaluate predictive factors for LR.

Results: 698 patients were identified. Median length of follow-up was 9.5 [5.3-13.9] years. LR occurred in 14.3% overall, 22% in medial and 12% in lateral tumor groups. On multivariate analysis, medial tumor location (HR 1.98, 95%CI 1.16 ? 3.38, p=0.01) and radiotherapy (HR 1.83, 95%CI 1.05 ? 3.15, p=0.03) predicted higher risk of LR while chemotherapy (HR 0.51, 95%CI 0.27 ? 0.97, p=0.04) and year of treatment (HR 0.92, 95% CI 088 ? 0.97, p&lt;0.001) predicted lower risk of LR.

Conclusion: Medial location of primary breast tumor was significantly associated with LR. We suggest considering this risk factor when selecting the best surgical approach and adjuvant therapy.

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Prioritizing melanoma surgeries to prevent wait time delays and upstaging of melanoma during the COVID-19 pandemic

Rebecca Lau*, BMSc and Katherine Aw*, BMSc, Carolyn Nessim, MD, MSc, FRCSC, FACS

Department of Surgery, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada
*These two authors contributed equally to this work.

Introduction: The COVID-19 pandemic has disrupted the delivery and usage of healthcare services in Canada. For aggressive cancers such as melanoma, prompt diagnosis, staging, and surgical management strongly impact prognosis. Considering the limited resources, emergency closures, and staffing shortages during the pandemic, our institution implemented a dedicated care pathway to prioritize cancer surgeries. We aim to assess whether this strategy was effective at preventing surgical wait time delays and upstaging of melanoma.

Methods: We retrospectively collected data of patients ? 18 years with biopsy-proven primary melanoma who underwent wide local excision between March 1, 2018-February 29, 2020 (pre-COVID) and March 1, 2020-February 28, 2022 (COVID). Patients with distant metastasis, recurrence, and unknown primary were excluded. Wait time from consult to surgery, tumor (T) and nodal (N) stage, and overall stage were collected.??

Results: We included 409 patients [pre-COVID (n = 203) and COVID (n = 206)] with a mean age of 62.2 ± 15.2 years and a male to female ratio of 1.3:1. Average wait time (days) ± SD to surgery was 38.1 ± 23.2 pre-COVID and 40.2 ± 24.0 COVID (p = .482). There were no differences found in T stage (p = .124), N stage (p = .177), or overall melanoma stage (p = .191).

Conclusion: These findings highlight the importance of streamlining melanoma surgery during a pandemic. As we emerge from the pandemic and the need arises to meet surgical backlogs including benign surgery, dedicated cancer surgery should maintain a priority to not negatively affect cancer outcomes.

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Population-Level Breast Reconstruction for Immigrant and Long-term Resident Women undergoing Breast Cancer Surgery

Olivia Lovrics MD MSc 1, Elena Parvez MD MSc FRCPC 1 2, David Kirkwood BScH MS 3, Christopher J Coroneos MD MSc FRCSC 4 5, Nicole Hodgson MD MSc FRCSC 1 2, Aristithes Doumouras MD MPH FRCSC 1 3, Jessica Bogach MD MSc FRCSC 1 2

1 Division of General Surgery, McMaster University, 2 Department of Surgery, Juravinski Hospital and Cancer Centre, 3 ICES, Toronto ON, 4 Division of Plastic Surgery, McMaster University, Hamilton, ON, 5 Division of Plastic Surgery, Juravinski Hospital and Cancer Centre, Hamilton, ON

Introduction: Immigrants are susceptible to marginalization, bias, difficulty navigating the health care system. Breast reconstruction surgery after mastectomy for breast cancer is associated with improved quality of life, and access to reconstruction is an important quality of care metric. This study aims to demonstrate differences in breast reconstruction after mastectomy for breast cancer between immigrant women and Canadian long-term residents in Ontario, Canada.

Methods: A retrospective population-based cohort-study using linked provincial administrative databases of patients with Stage I-III breast cancer diagnosed between 2010-2016. Immigration status was obtained from the federal Immigration Refugee and Citizenship Canada database. Variables including, age, stage, co-morbidity, socio-economic factors, cancer histology, and treatments were collected. Data on treatment facility and characteristics were collected. Proportion of immigrant and Canadian long-term resident women undergoing breast reconstruction were compared. Multivariable analysis was performed to adjust for patient, tumour, and treatment characteristics.

Results: 46,930 long-term residents and 7,160 immigrant women. Immigrant women were younger at diagnosis (median 52 vs. 63 years, p&lt;0.01), and more likely to have Stage III disease (16.8% vs. 13.9%, p&lt;0.01). Immigrant women were more likely to be treated at urban, high-volume breast surgery centers with plastic surgeons. 2,196 immigrant women (30.7%) and 13,656 (29.1%) Canadian-long-term residents underwent mastectomy. On univariate analysis, immigrant women were more likely to undergo breast reconstruction surgery overall when compared to Canadian long-term residents (21.4% vs. 18.9%. p&lt;0.01) but were less likely to undergo delayed reconstruction (13.9% vs. 13.3%, p=0.42). Region of origin, but not time in Canada, were significantly associated with reconstruction uptake. On multivariable logistic regression, immigrant women were less likely to undergo reconstruction when adjusting for baseline covariates [OR 0.59 (0.51-0.68)], including patient characteristics, tumour characteristics, and location.

Conclusion: Immigrant women were more likely to undergo breast reconstruction after mastectomy on univariate analysis, but when adjusting for baseline covariates, the inverse relationship was found. This may be that immigrant women are more often treated at urban, high-volume centers with availability of plastic surgeons, and as a result undergo less reconstruction than would be expected when accounting for these factors.

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Is Rectosigmoid a distinct primary site of colorectal cancer?

Paul Savage, MD, PhD 1, Carol J. Swallow, MD, PhD 1 2, David P. Cyr, MD, MSc 1, Sameer Shivji, MD 3, James Conner, MD, PhD 3, Richard Kirsch, MBChB, PhD 3, Anand Govindarajan, MD, MSc 1 2, Satheesh Krishna, MD 4

1 Division of General Surgery, Department of Surgery, University of Toronto, Toronto, Ontario, Canada, 2 Department of Surgical Oncology, Mount Sinai Hospital, Toronto, Ontario, Canada, 3 Department of Pathology and Laboratory Medicine, Sinai Health System, Toronto, Ontario, Canada, Richard Kirsch, MBChB, PhD, 4 Medical Imaging, University of Toronto, Toronto, Ontario

Introduction: It is unclear whether primary colorectal cancer (CRC) located at the junction between the sigmoid colon and upper rectum (?rectosigmoid?) should be treated as colon or rectal cancer.

Methods: Consecutive patients who underwent resection of a primary colorectal adenocarcinoma at Mount Sinai Hospital from 2011-2016 were identified from a prospective database (N=800). For tumours distal to the left colon (N=400), pre-treatment CT ± MRI images were reviewed to classify site of primary tumour based on relationship to the sigmoid take-off as defined by D?Souza et al. (Ann Surg 2019). Clinicopathologic features and patient outcomes were compared using Kruskal-Wallis, ?2, Kaplan-Meier and log-rank.

Results: Patients were classified as having primary sigmoid (N=147), rectosigmoid (N=89) or upper rectal (N=70) cancer. The proportion who received neoadjuvant therapy was similar for rectosigmoid vs. upper rectal (53% vs. 54%), and less for sigmoid cancer (17%)(p&lt;0.0001). The early re-operation rate was higher following resection of rectosigmoid vs. sigmoid and upper rectal cancer (8% vs. 3% and 0%, p=0.02). Positive resection margins were more frequent for rectosigmoid vs. upper rectal and sigmoid cancer (16% vs. 4% and 5%, respectively p=0.008). At median follow-up of 4.9 years (IQR 2.7-6.0), local recurrence in patients with rectosigmoid cancer (13%) approximated that for upper rectal cancer, which was higher than sigmoid cancer (HR 7.6, 95%CI 2.2-25.7 rectosigmoid vs. sigmoid, p=0.002).

Conclusion: Rectosigmoid cancers account for >10% of all CRC and carry a notably high risk of positive resection margins and local recurrence. Management of rectosigmoid cancer should be distinct from that of colon cancer.

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High Tumour Microenvironment Score is associated with improved overall survival in gastric cancer patients receiving chemotherapy

Daniel Skubleny, MD, PhD , Gina R. Rayat, Msc, PhD, Dan E. Schiller, MD, MSc, Jennifer Spratlin, MD, Sunita Ghosh, PhD

University of Alberta

Introduction: Gastric cancer remains an aggressive disease and is the third most common cause of cancer death worldwide. Molecular heterogeneity in gastric cancer is associated with variable treatment responses to cytotoxic chemotherapy. We evaluated whether complex molecular classification systems in gastric cancer could inform subgroup treatment effects related to chemotherapy.

Methods: Molecular subtypes of the Cancer Genome Atlas (TCGA), Asian Cancer Research Group (ACRG), and Tumour Microenvironment (TME) Score were learned from whole transcriptome data using artificial intelligence and applied to a public cohort of 2,202 gastric cancer patients. Bias between gene expression measurement technologies was mitigated using feature-specific quantile normalization. We used propensity score matching to identify comparable patients treated with and without chemotherapy. Matching covariates included molecular subtype scores and clinical characteristics. We assessed survival outcomes using multivariable Cox proportional hazards models.

Results: Our matched cohort included 237 patients treated with chemotherapy and 158 patients who did not receive chemotherapy. The absolute standardized mean difference between covariates was &lt;0.1. Increasing TME high score was associated with improved survival in patients receiving chemotherapy compared to those that did not (Hazard Ratio 0.47 [95% CI 0.29, 0.74], Interaction p=0.04). TCGA and ACRG molecular subtypes as well as tumour stage and location provided no subgroup treatment effect related to chemotherapy.

Conclusion: In a propensity score matched cohort, we identify that gastric cancer patients who receive cytotoxic chemotherapy achieve greater overall survival as the TME score increases. These data could improve patient selection for chemotherapy but must be further validated in a prospective study.

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Surgical decision making in young breast cancer patients: Impact of pre-treatment surgical preference congruence with final surgical treatment on psychosocial health

Melissa L. Wood, MD, BSc, MSc, FRCSC 1, Dr. May Lynn Quan, MD, BSc, MSc, FRCSC 1, Dr. Kelly Metcalfe, RN, PhD 2, Dr. Yuan Xu, MD, PhD 1, Dr. Susan Isherwood, PhD 1, Yue (Flora) Yang, MDSA 1, Xing Wang, MSc

1 University of Calgary, 2 University of Toronto

Introduction: Type of breast surgery in young women is known to impact quality of life. We sought to determine if congruence between pre-treatment surgical preference and final surgery had an impact on psychosocial health.

Methods: Women &lt; 41 with breast cancer in the RUBY study. Patient demographics, pre-consult surgical preference, surgery type, psychosocial outcomes, and congruence were collected. Outcomes were decision regret, anxiety, PHQ-9, and BreastQ. Univariate data analyses were performed.

Results: Among 1000 women, median age was 37 years; 39.2% had breast conserving surgery and 60.8% mastectomy. In total, 326 women expressed congruence, 206 non-congruence, while 468 had no preference. Reasons for mastectomy differed significantly; ?what I wanted? (congruent 87.4%, non-congruent 55.7%, no preference 70.9%; p &lt; 0.001) and ?surgeon recommended? (congruent 39.4%, non-congruent 74.5%, no preference 60.3%; p &lt; 0.001). At baseline, global anxiety was significantly higher (p = 0.02) in the non-congruent compared to the congruent/no preference groups. Depression, decision regret, and overall anxiety were not significantly different post-surgery. When stratified by surgery type, using the BreastQ assessment, post-treatment breast satisfaction (p = 0.03), and psychosocial wellbeing (p = 0.05), were significantly poorer in the non-congruent group.

Conclusion: Non-congruent status of preop preference to actual surgery is significantly associated with higher baseline global anxiety and poorer psychosocial wellbeing. Awareness of these psychosocial implications may provide an opportunity to develop targeted support.

CSSO-01

Incidence, Timing and Outcomes of Venous Thromboembolism in Patients Undergoing Surgery for Esophagogastric Cancer: A Population-Based Cohort Study

Hanna Nader, Williams Erin, Kong Weidong, Fundytus Adam, Booth Christopher, Patel Sunil, Caycedo-Marulanda Antonio, Chung Wiley, Nanji Sulaiman, Merchant Shaila, Queen's University

Background: Abdominal surgery and chemotherapy are risk factors for venous thromboembolism (VTE) in patients with cancer, but their contribution in patients with esophagogastric cancer is unclear. We quantified VTE risk, identified risk factors for VTE, and determined the association between VTE and survival in patients undergoing surgery for esophagogastric cancer.

Methods: A population-based retrospective cohort study was conducted using linked administrative databases. We used the Ontario Cancer Registry to identify patients with esophageal or gastric cancer between January 2007 and December 2016 who underwent surgery. First VTE event was captured at clinically relevant timepoints 180 days before and after surgery. Logistic regression was used to identify factors associated with VTE with odds ratios (OR) and 95% confidence intervals (CI) reported. Cox proportional hazards regression models were used to estimate associations between covariates and overall survival (OS) and cancer-specific survival (CSS).

Results: Of the 4,894 patients who had esophagectomy or gastrectomy, 8% (n=383/4,894) had a VTE. VTE risk was 2.5% (n=123/4,894) 180 days before surgery, 2.8% (n=138/4,894) within 30 days of surgery and 2.5% (n=122/4,894) from 31- ≤180 days after surgery. Of the patients with VTE within 30 days of surgery, 34% (n=47/138) were diagnosed after hospital discharge. Pre-operative chemotherapy was associated with VTE 180 days before surgery (OR 3.84, 95% CI 2.41, 6.11). Increased hospital length of stay (LOS) was associated with VTE 30 days after surgery (OR 1.08, 95% CI 1.02, 1.14, per week). In adjusted models VTE was associated with inferior OS (HR 1.36, 95% CI 1.13, 1.63) and CSS (HR 1.42, 95% CI 1.16, 1.75).

Conclusion: Highest VTE risk is within 30 days of surgery with one third diagnosed after hospital discharge. Longer hospital LOS and pre-operative chemotherapy are associated with increased VTE risk. VTE is an independent risk factor for inferior survival in patients with esophagogastric cancer.

CSSO-04

Omission of Axillary Staging and Survival in Elderly Women with Early Stage Breast Cancer: A Population-Based Cohort Study

Castelo Matthew, Hansen Bettina, Paszat Lawrence, Baxter Nancy, Scheer Adena , University of Toronto

Introduction: Surgical axillary staging in women ≥ 70 years with early stage breast cancer is controversial. Older randomized evidence has not shown axillary staging improves survival, but recent observational studies have been mixed and widespread de-implementation of the practice has not occurred. The aim of this study was to determine if axillary staging is associated with survival in elderly women with breast cancer.

Methods: This was a population-based cohort study using the SEER registry. Women ≥ 70 years diagnosed with T1-T2 invasive breast cancer from 2005 to 2015 were included. Overlap propensity score weighting was used to adjust for confounders. Overall survival (OS) was determined and hazard ratios (HRs) reported with 95% confidence intervals (CIs). Breast cancer-specific survival (BCSS) was determined using competing risks analysis, and subdistribution hazard ratios (sdHRs) reported. Additional adjustment was performed for receipt of chemotherapy and radiotherapy.

Results: 144,329 elderly women were included, of whom 22,621 (15.7%) did not undergo axillary staging. After overlap propensity score weighting, baseline characteristics were well balanced between the two groups. Women who did not undergo axillary staging were significantly less likely to receive chemotherapy (adjusted RR 0.58, 95% CI 0.54 - 0.62) or radiotherapy (adjusted RR 0.53, 95% CI 0.52 - 0.54), and had significantly worse OS (adjusted HR 1.22, 95% CI 1.19 - 1.25), and breast cancer-specific survival (adjusted sdHR 1.14, 95% CI 1.08 - 1.21) compared to those that had staging. Subgroup analyses restricted to women with ER+/HER2- tumours showed similar findings to the main analysis (adjusted sdHR 1.17, 95% CI 1.05-1.31).

Conclusion: These findings suggest elderly women with early-stage breast cancer who do not undergo axillary staging experience worse outcomes. Reasons for this disparity may be multi-factorial and require further investigation.

CSSO-05

Patients' Experiences Receiving Cancer Surgery during the COVID-19 Pandemic: A Qualitative Study

Pook Makena1, Najafi Ghezeljeh Tahereh 2, Lapointe-Gagner Maxime3, Nguyen-Powanda Philip3, Elhaj Hiba4, Rajabiyazdi Fateme 5, Lee Lawrence4, Feldman Liane S. 4, Fiore Jr. Julio6

1 Division of Experimental Surgery, McGill University, Montreal, QC, Canada, 2 School of Nursing and Midwifery, Iran University of Medical Sciences, Tehran, Iran., 3 Division of Experimental Surgery, McGill University, Montreal, QC, Canada., 4 Steinberg-Bernstein Centre for Minimally Invasive Surgery and Innovation, McGill University Health Centre, Montreal, QC, Canada., 5 Department of Systems and Computer Engineering, Carleton University, Ottawa, ON, Canada., 6 Centre for Outcomes Research and Evaluation, Research Institute of the McGill University Health Centre, Montreal, QC, Canada.

INTRODUCTION: In response to COVID-19, Quebec repurposed surgical care infrastructure and delayed many elective cancer surgeries. However, postponing cancer surgery is known to cause anxiety and distress. A qualitative study was conducted to understand patients' experiences receiving surgical cancer treatment during the COVID-19 pandemic.

METHODS: Patients who underwent general surgery for cancer at the McGill University Health Centre between March 2020 and January 2021 were invited to one-to-one interviews. Patients were purposefully selected for maximum variation using quota sampling (i.e., targeting delay status, pandemic phase, cancer site, and clinical/demographic characteristics) until interviews produced no new information (i.e., thematic saturation). Interviews were conducted using a semi-structured guide, audio-recorded, transcribed verbatim, and analyzed independently by two researchers. Data were managed using MAXQDA2020 and analyzed according to inductive thematic analysis.

RESULTS: Interviews were conducted with 20 patients [mean age 64; male (n=10); cancer sites: breast (n=8), skin (n=4), hepato-pancreato-biliary (n=4), colorectal (n=2), and gastro-esophageal (n=2)]. Surgery was delayed for 14 patients: 8 by the hospital, 4 by the patient, and 2 due to a positive COVID-19 test. Thematic analysis revealed that patients considered their susceptibility to infection, hospital safety measures, and burden on healthcare resources when determining willingness to undergo surgery. Patients weighed these risks against the urgency of their health condition and recommendations of their provider. Changes to the hospital environment (e.g., COVID-19 preventative measures) and deviations from expected treatment (e.g., alternative treatments, remote consultations, rescheduled care) caused diverse psychological responses, ranging from increased satisfaction to severe distress. Patients employed coping strategies (e.g., reframing care interruptions, communicating with clinicians, information seeking) to mitigate distress.

CONCLUSION: In summary, changes in care during the pandemic elicited diverse psychological responses from patients undergoing cancer surgery. Patient coping was facilitated by open, consistent communication with clinicians, emphasizing the importance of patient-centered discussions regarding surgical delays within and beyond the pandemic.

CSSO-08

Quality of Narrative Central and Lateral Neck Dissection Reports for Thyroid Cancer Treatment Suggests Need for a National Standardized Synoptic Operative Template

Watanabe Akie1, Prisman Eitan 1, Mitmaker Elliot2, Walker Ross3, Wu Jonn1, Nguyen Anne1, Wiseman Sam1

1 University of British Columbia, 2 McGill University, 3 Queen's University

Introduction: Consistent documentation of anatomic structures in central (CND) and/or lateral neck dissections (LND) is important for effective communication between multidisciplinary teams. This study aimed to investigate the current completeness of CND and LND narrative operative reports.

Methods: Twenty-nine surgeons from 6 provinces who treat malignant thyroid disease provided de-identified CND and LND narrative reports. Important report elements were identified based on recommended items from prior literature and summarized using descriptive statistics for both CND and LND (stratified by dissection level).

Results: Amongst 53 CND reports, 66% and 17% documented level VI and VII dissections, respectively. 25% did not indicate the level(s) of dissection. Other than the recurrent laryngeal nerve(s) (96%), status of critical structures including the carotid artery(s) (43%), superior laryngeal nerve(s) (15%), and innominate artery(s) (9%) were insufficiently reported. Amongst 23 LND reports, 9%, 83%, 83%, 87%, and 61% documented level I, II, III, IV, and V dissections, respectively. Status of the sternocleidomastoid muscle (91%) and internal jugular vein (91%) were frequently reported across all dissection levels, while only 39% recorded the presence or absence of a chyle duct leak. For level I dissections (N=2), the status of the submandibular gland(s), lingual nerve(s), and hypoglossal nerve(s) were reported 100% of the time. Similarly, the integrity of the spinal accessory nerve(s) (86%) was frequently reported for level V dissections (N=14). In contrast, important structures such as the vagus nerve(s) (50%), cervical rootlets (27%), and occipital artery(s) (5%) for level II/III dissections (N=22) and the thoracic duct (20%) for level IV dissections (N=20) were inadequately reported.

Conclusion: Current narrative operative reporting fails to consistently document the status of important structures dissected in the central and lateral necks. Development of an accepted standardized national synoptic operative template may enhance reporting completeness and facilitate improved quality of patient care across multidisciplinary teams.

CSSO-09

Transoral Endoscopic Thyroidectomy Vestibular Approach (TOETVA): Indications and Technique

Saravana-Bawan Bianka1, Hong Dennis2, Gupta Michael2, Pasternak Jesse1

1 University Health Network, University of Toronto, 2 St. Joseph's Healthcare, McMaster University

INTRODUCTION: Thyroid surgery has progressed from large collar incisions to more cosmetically sensitive dimensions. Nevertheless, scarring remains a prominent concern among patients specifically from communities where neck scar has substantial stigma. To address these concerns, alternatives to traditional approach were explored, such as trans-axillary and facelift approaches.

METHODS: These approaches, however, require robotic instrumentation, considerable extra training, and cutaneous incisions. Comparatively, transoral endoscopic thyroidectomy vestibular approach (TOETVA) uses common laparoscopic equipment and has minimal learning curve for endocrine surgeons trained in thyroid surgery and laparoscopy.

RESULTS: In a recent Johns Hopkins review, learning curve for TOETVA was noted to be 7 to 11 cases. Once learning curve has plateaued, TOETVA operative times are not significantly longer than that of traditional thyroidectomy, demonstrating an average of 78 compared to 64 minutes for thyroid lobectomy and 135 compared to 103 minutes for total thyroidectomy. This approach is comparatively easy for thyroid surgeons to learn as it employs the traditional thyroidectomy planes. Importantly, there are no increased risks of complications in comparison to traditional thyroidectomy as seen in the largest series. Paratracheal tissue, including parathyroid glands, are easily observed and the recurrent laryngeal nerves (RLNs) are visualized in a plane which represents a more favorable angle with magnified view than that of traditional open approach. Patient selection is key as benign nodules less than 6cm with thyroid lobe no larger than 10cm are recommended for TOETVA. As expertise and familiarity increases, these limits may be pushed.

CONCLUSION: Originally performed for benign disease alone, TOETVA is now also performed for small (less than 2cm), well differentiated thyroid cancers. In addition to these criteria, patients with a short mental distance and good neck extension should be considered. The only contra-indication to TOETVA is the inability to tolerate surgery or general anesthetic. This video demonstrates TOETVA performed at our centre.

CSSO-11

Molecular Landscape of Early-Stage Breast Cancer with Nodal Metastasis

Brackstone Muriel, Ghasemi Farhad

Western University

Introduction: The presence of axillary lymph-node metastasis is an important prognostic factor in breast cancer, and serves as the basis of important treatment decisions such as neoadjuvant or adjuvant systemic therapy. Clinical evaluation of axilla lymphadenopathy is inaccurate, leading to sentinel lymph-node biopsies (SLNBs) to stage the disease. SLNB is associated with morbidity for the patients, excludes the possibility of future SLNB, and requires health-care resources. As such, a better understanding of molecular processes leading to axillary metastasis in breast cancer is important and can aid us in pre-operative prediction of nodal involvement.

Methods: A multi-platform comparison of early-stage breast tumours (≤ 5cm) in patients undergoing SLNB was compared using data from The Cancer Genome Atlas (TCGA) project. The comparison between 250 node-negative and 162 node-positive early-stage breast tumours revealed 766 statistically significant differentially expressed mRNAs and 40 differentially expressed miRNAs.

Results: Distinct heterogeneity existed between the four molecular subtypes (Luminal A, Luminal B, Basal, Her2) of breast cancer. Only 33.2% of the discovered differentially expressed mRNAs were either over-expressed or under-expressed consistently across all subtypes with nodal involvement. Pathway enrichment analysis highlighted several pathways including immune-response and chromatin assembly. There were no statistically significant differences in single nucleotide variations, copy number alterations or protein expression between node-negative and node-positive patients.

Conclusions: The potential molecular signatures identified in this study may prove valuable in the development of predictive models of axillary involvement, and highlight the importance of a subtype-specific approach to breast cancer.

CSSO-14

Association between Patient-Reported Symptoms and Health Care Resource Utilization: A First Step to Develop Patient-Centred Value Measures in Cancer Care

Hirpara Dhruvin 1, Eskander Antoine 2, Coburn Natalie2, Sutradhar Rinku3, Chan Wing 3, Hallet Julie 2

1 University of Toronto, 2 Sunnybrook Hospital, 3 ICES

Introduction: Value of care is defined as patient-relevant outcomes achieved per dollar spent. Patient Reported Outcomes (PROs) offer a unique lens into cancer care; their relationship with cost and resource utilization, however, is yet to be defined. We examined the association between PROs and health resource utilization (HRU) in the year after cancer diagnosis, with a view to develop PRO-based measures of Value.

Methods: We conducted a population-based cohort study of adults with cancer (2008-2019). The exposure was symptom burden measured using Edmonton Symptom Assessment System (ESAS) scores. The outcome was total healthcare cost within 30-days of ESAS reporting, as a metric for HRU. HRU was further stratified into cancer-directed therapies (i.e., chemotherapy and radiation) or ancillary services including emergency department visits, complex continuing care, homecare, and inpatient mental health. Linear regression models with log-transformed costs examined the association between ESAS scores and outcomes adjusting for potential confounders.

Results: 1,728,025 ESAS surveys from 285,924 patients were analyzed. Gastrointestinal, breast and CNS cancers were the most resource intensive cancers with median 30-day costs (CAD) after ESAS of $85,000, $81,000, and $78,000, respectively. Each 10-point increase in total ESAS score (0 to 90) was associated with a 9.4% decrease in the cost of cancer-directed therapies. Conversely, each 10-point increase was associated with an 18% increase in costs of ancillary care. The association between symptom burden and HRU is depicted in Figure 1.

Conclusions: High symptom burden was associated with decreased use of cancer-directed therapy but increased use of ancillary care, indicating interruptions to oncologic treatment. Proactive symptom management may mitigate unnecessary HRU and facilitate cancer-directed therapies. Future work will further explore the relationship between PROs and HRU/costs to develop a PRO-based measure of Value in cancer care.

CSSO-12

Beta Testing of a Risk-Stratified Patient Decision Aid to Facilitate Shared Decision Making for Postoperative Extended Thromboprophylaxis in Patients Undergoing Major Abdominal Surgery for Cancer

Ivankovic Victoria1, Delisle Megan1, Stacey Dawn2, Abou-Khalil Jad2, Balaa Fady3, Bertens Kimberly2, Dingley Brittney3, Martel Guillaume2, McAlpine Kristen4, Nessim Carolyn2, Tadros Shaheer3, Carrier Marc2, Auer Rebecca2

1 The University of Ottawa, 2 Ottawa Hospital Research Institute, 3 University of Ottawa, 4 University of Toronto

Background: We previously developed a novel patient decision aid (PtDA) to facilitate shared decision-making between patients and clinicians when deciding whether to use extended-duration thromboprophylaxis or not for four weeks after major abdominopelvic surgery for cancer. Our PtDA was found to be acceptable with patients and clinicians. The objective of this study was to build on our previous work by evaluating the effectiveness of our PtDA.

Methods: Patients undergoing major abdominal surgery for cancer at an academic centre were enrolled in this pre- post-test study. Institutional ethics approval was obtained. All outcomes were measured using previously psychometrically validated surveys. The primary outcome was change in decisional conflict. Secondary outcomes included readiness to make a decision, confidence in decision making, and change in patient knowledge of the health care decision. A sample size calculation determined a total of 17 patients were required to demonstrate the PtDA meaningfully reduced decisional conflict using a paired t-test.

Results: A total of 17 patients were recruited. The median age was 68 years old (range 28-82) and the majority of patients were male (13/17, 76.5%). Based on the Caprini Score, 1 patient was low risk, 6 were moderate risk, 5 were high risk, and 5 were very high risk of developing a venous thromboembolism. The median pre-PtDA decisional conflict score was 2.4, compared to a post-PtDA score of 1.3 (p<0.01). The median score for confidence in decision-making was 86.4, corresponding to high confidence. Median knowledge scores increased from 50% to 75%. Median score for readiness to make a decision following the PtDA was 90, indicating a high perceived level of preparedness to make a decision.

Conclusions: The PtDA significantly reduced decisional conflict and was effective at improving the parameters of patients' decision-making abilities. Patients demonstrate high confidence for decision-making, and indicate they are prepared to decide after using the PtDA.

CSSO-16

Why Do Patients with Non-metastatic Primary Retroperitoneal Sarcoma Not Undergo Resection?

Ng Deanna1, Acidi Belkacem 2, Johnston Wendy3, Callegaro Dario4, Brar Savtaj3, Gladdy Rebecca3, Chung Peter 5, Catton Charles5, Khalili Korosh6, Honore Charles2, Swallow Carol3

1 University of Toronto, 2 Gustave Roussy, 3 Mount Sinai Hospital, 4 Istituto Nazionale dei Tumori, 5 Princess Margaret Cancer Centre, 6 University Health Network

INTRODUCTION: Resection is the mainstay of management of primary RPS, but an unknown proportion of patients do not undergo resection even though the tumour is localized. Very few centres systematically collect data regarding RPS patients who do not come to resection. We investigated the incidence of and underlying reasons for non-resection, using prospectively maintained data from two high volume sarcoma centres.

METHODS: Consecutive patients who presented with primary RPS and no distant metastases on staging imaging were included (n=276; 2012-2017).

RESULTS: Of these, 188 (69%) underwent resection, while 88 (31%) did not. Patients who did not have resection were older (Table), and approximately half had significant comorbidities (n=46) and/or poor performance status (n=41). Interestingly, the median maximum tumour size was smaller in the non-resected cohort. The 88 patients who did not undergo resection were divided into 3 groups. Group A (n=23) were patients who were deemed technically unresectable due to extensive involvement of the SMA/SMV, portal vein, aorta, spinal canal or mediastinum. Group B (n=40) comprised patients who received either no (n=29) or brief (n=11) active treatment, with no short-term (3 months) progression of disease. Group C (n=25) were patients who progressed on what was planned to be cytoreducing preoperative treatment (chemotherapy and/or XRT) (n=25). For the entire cohort of 88 non-resected patients, median OS was 13 months and 3yr OS was 35% (95% CI 25-48%) (Kaplan Meier). Patients in Group A (technically unresectable) and Group B (no progression) had similar OS, but Group C (progression on treatment) showed a rapid decline in OS (Figure, p=0.007). Nearly one-third of patients who presented with non-metastatic primary RPS did not ultimately undergo resection.

CONCLUSION: Progression of disease on planned preoperative treatment was associated with very limited survival, revealing adverse biology. The ability to predict early progression would facilitate adaptive response to guide innovative therapeutic approaches.

CSSO-17

Loss of FAM46C Expression Predicts Inferior Post-resection Survival and Induces Ion Channelopathy in Gastric Adenocarcinoma

Luu Shelly1, Fu Ning2, Kazazian Karineh1, Pacholczyk Karina3, Ng Deanna1, Swett-Cosentino Jossie4, Savage Paul1, Shibahara Yukiko5, Kalimuthu Sangeetha1, Espin-Garcia Osvaldo1, Conner James1, Yeung Jonathan1, Darling Gail6, Swallow Carol1

1 University of Toronto, 2 University of Ottawa, 3 Lunenfeld-Tanenbaum Research Institute, 4 Brockville General Hospital, 5 Kitasato University School of Medicine, 6 Dalhousie University

INTRODUCTION: More precise delineation of recurrence risk and pattern would facilitate personalized use of adjunctive therapies in patients with gastric adenocarcinoma (GCa). Our aim is to discover high fidelity markers of risk, and novel therapeutic targets.

METHODS: Tumour (T) and paired normal mucosa (NM) samples were microdissected from curatively resected GCa specimens from 158 patients (2001-2017). RNA was extracted and differential gene expression correlated with patient outcome. Disease-specific survival (DSS) was estimated by the Kaplan-Meier method and hazard ratios estimated with Cox Regression.

RESULTS: Median age of the study cohort was 70 years, with a median post-resection follow-up time of 31 months (IQR 12-73) and 3-year DSS of 66%. We explored potential markers of recurrence risk by performing a directed screen of 55 members of the oncogene Plk4 interactome. This revealed reduced expression of the nucleotidyl transferase FAM46C in tumour tissue in 94% of patients.

CONCLUSION: Retention of FAM46C expression (T/NM≥median, n=79) was associated with superior 3-year DSS (75% vs 57% in T/NM

CSSO-18

Liver-Directed Therapy of Neuroendocrine Liver Metastases

Meloche-Dumas Léamarie1, Mercier Frédéric2, Barabash Victoria3, Law Calvin4, Coburn Natalie4, Singh Simron4, Myrehaug Sten4, Chan Wing5, Hallet Julie4

1Université de Montréal, 2Centre hospitalier de l'Université de Montréal (CHUM), 3Sunnybrook Research Institute, 4Odette Cancer Centre/Sunnybrook Health Sciences Centre, 5Cancer Research Program, Institute of Clinical Evaluative Sciences (ICES)

INTRODUCTION: The optimal therapy sequencing for metastatic neuroendocrine tumors (NETs) remains undefined. Recent advances in systemic therapies may have changed approaches. Better understanding in patterns of care is necessary to assess and design treatment strategies.

METHODS: We examined the use of factors associated with liver-directed therapy over time. We conducted a population-based study of metastatic NETs over 2000-2019. Outcomes were use of liver-directed therapy, sub-divided into liver resection and embolization. Bi-yearly incidence rate of use in eligible patients (alive and no prior liver-directed therapy) was assessed. Multivariable Poisson models examined factors associated with use of liver-directed therapies.

RESULTS: Of 5,159 metastatic NETs, 922 patients (16.7%) received liver-directed therapy (461 embolizations, 329 resections, 132 dual therapy) at median of 35 days (IQR:0-490) after metastatic diagnosis. Incident use of liver embolization increased after 2013 to reach 72% in 2018-19. Incident use of liver resection followed a similar trajectory up to 94% in 2018-19 (Figure). Gastro-entero-pancreatic primary NET (relative risk - RR 5.69; 95%CI 3.76-8.60), female sex (RR 1.25 95%CI 1.05-1.48), year of diagnosis (RR 1.32; 95%CI 1.04-1.68 for 2007-2015), and lower socioeconomic status (RR 0.93, 95%CI 0.87-0.98 by incremental material deprivation quintile) were independently associated with liver resection. Gastro-entero-pancreatic primary NET (RR 2.8, 95%CI 2.2-3.7), socioeconomic status (RR 0.94, 95%CI 0.89-0.99 by quintile) and year of diagnosis (RR 0.71, 95%CI 0.59-0.85 for 2007-15 and RR 0.61, 95%CI 0.50-0.75 2016-2020) were independently associated with risk of liver embolization.

CONCLUSION: Receipt of liver-directed therapies for metastatic NETs has increased over time in unadjusted analysis. However, there was lower risk of liver embolization in most recent time periods, but higher risk of resection. Socio-economic status represented an independent factor for lower likelihood of liver-directed therapies. Further characterization of timing and outcomes of liver-directed therapy, with an equity lens, is warranted to define the optimal sequencing.

CSSO-20

Molli® for Excision of Non-palpable Breast Lesions: A Case Series

Eom Ashley, Muhn Narry, Heller Barbara, Lovrics Peter

McMaster University

INTRODUCTION: Nonpalpable breast lesions require intraoperative localization. Magnetic Occult Lesion Localization Instrument (MOLLI®) is a novel localization technique that employs ferromagnetic marker technology, detected through a hand-held probe for intra-operative lesion localization, without the limitations of radioactive seeds or wire localizations.

METHODS: We examined the clinical outcomes of MOLLI®-guided localization of non-palpable breast lesions at a single institution. A consecutive sample of 30 patients with non-palpable breast lesions underwent lumpectomy with or without sentinel lymph node biopsy. MOLLI® markers were placed pre-operatively by a breast radiologist under sonographic or stereotactic mammogram guidance. The hand-held probe was used to localize the marker signal intra-operatively. Complete excision of the marker and lesion were confirmed with specimen radiography. Patient demographics, operative, pathological data were collected retrospectively from electronic medical records.

RESULTS: 7 of 30 patients had multifocal disease requiring multiple markers. One patient had bilateral lesions. One patient failed marker placement as it did not deploy within a cystic lesion. Thus, a total of 29 patients and their 36 lesions were analyzed and summarized in Table 1. One pathologic margin was involved by DCIS, but clear of invasive carcinoma. Marker migration did not occur. Post-operatively, two patients developed cellulitis and one patient developed hematoma.

CONCLUSION: Our study is the second series to demonstrate the MOLLI® marker to be an effective alternative to radioactive seeds in the localization of non-palpable breast lesions. All markers were successfully identified and yielded surgical specimen with margins clear of invasive carcinoma. The markers were placed up to 47 days pre-operatively without complications, allowing for flexibility in scheduling without the resources required for radiation safety. One marker failed to deploy within a cystic lesion; the deployment mechanism was subsequently altered to correct this. The novel MOLLI® technology guides surgery with dynamic audible signals, visual guidance, and precise distance measurements, enabling efficient localization.

CSSO-24

Absence of Benefit of Routine Surveillance in Very Low and Low Risk Gastric Gastrointestinal Stromal Tumors

Schmitz Erika1, Apte Sameer2, Nessim Carolyn 3

1 University of Ottawa Faculty of Medicine, 2 University of Ottawa, 3 The Ottawa Hospital, Department of Surgical Oncology

INTRODUCTION: Gastric gastrointestinal stromal tumors (GIST) are mesenchymal neoplasms with heterogenous malignant behavior. Adjuvant therapy and routine surveillance is guided by the risk of recurrence, which is largely determined by tumor location, mitotic rate, size and intra-operative tumor rupture. Recurrence after surgical resection of very low and low risk gastric GISTs is exceedingly rare. Despite this, the National Comprehensive Cancer Network suggest abdominopelvic cross-sectional imaging every 3-6 months for 3-5 years then annually, while the European Society for Medical Oncology state that routine follow-up may not be warranted in very low risk GIST and the benefit of routine follow-up is not known. Consequently, the aim of this study is to characterize the patterns of recurrence amongst the low and very low risk gastric GISTs, and determine the value of surveillance at our center.

METHODS: Adult patients with gastric GIST who underwent surgical resection at a single tertiary care center between 2010-2020 were evaluated. Demographics, clinical presentation, radiologic and endoscopic findings, pathological results and surveillance data were collected and analysed.

RESULTS: 139 patients underwent resection of a gastric GIST and were eligible for inclusion. According to the National Institute of Health modified classification system, 8.6% (n=12) were considered very low risk, 37.4% (n=52) low risk, 36% (n=50) intermediate risk and 18% (n=25) high risk. We observed one recurrence in the intermediate risk group at 4 years (2%) and two within the high-risk groups at 2 and 3 years (8%), all of which were non-perforated, asymptomatic and detected on routine surveillance imaging. Amongst the very low risk group, three were discharged to their family physician for surveillance, and the remaining 77.8% (n=7) underwent surveillance with cross sectional abdominal imaging and 33.3% (n=3) with additional chest imaging, respectively. Amongst the low-risk group, ten patients were discharged to their family physician for surveillance, and the remainder 57.1% (n=24) underwent surveillance with cross sectional abdominal imaging and 30.9% (n=13) with additional chest imaging, respectively. Nine patients of the low-risk group underwent endoscopic surveillance. After a median of 37.1 and 34.3 months surveillance within the very low and low risk groups, we observed no recurrences and detected no additional malignancies.

CONCLUSION: There were no recurrences of very low risk and low risk gastric GIST after surgical resection in this single site population. While considering cost-effectiveness and in the absence of randomized control trials, this evidence may support that routine radiologic and endoscopic surveillance may not be warranted amongst these subgroups.

CSSO-26

Active Surveillance for DCIS of the Breast: Qualitative Interviews with Patients and Physicians

Newman-Bremang Jieun, Look Hong Nicole, Gagliardi Anna, Nyhof Bryanna

University of Toronto

INTRODUCTION: Multiple international trials are currently investigating the safety of active surveillance (AS) for low-risk DCIS, where surgical excision is offered only in the case of progression to invasive cancer. The objective of this study was to explore views on acceptability of AS for low-risk DCIS from DCIS survivors and physicians.

METHODS: Women with a history of DCIS were recruited using purposive sampling and interviewed in five focus groups. Concurrently, physicians specializing in breast cancer care were recruited via purposive and snowball sampling and interviewed via semi-structured telephone interviews. All interviews were conducted using interview guides that were created and pilot tested as part of a larger study on patient centered care on DCIS. The responses were recorded and transcribed verbatim. Data was analyzed iteratively with qualitative descriptive analysis and constant comparative analysis was used to extract dominant themes.

RESULTS: We interviewed a total of 35 women in five focus groups held in 5 provinces in Canada (British Columbia, Alberta, Saskatchewan, Ontario, Nova Scotia), as well as 40 physicians from general surgery, surgical oncology, medical oncology, radiation oncology and radiology. The majority of DCIS survivors and physicians were hesitant towards active surveillance, and risk of missed invasive disease was the top concern by both patients and physicians. Both groups recognized that it is not yet the standard of care, and addressed the need for tools to predict the risk of progression prior to recommending AS.

CONCLUSION: The DCIS survivors and physicians were overall aligned in their hesitancy for AS in its current state. If AS were to be proven to be safe, these important considerations should be included for an effective implementation of AS for DCIS.