The impact of reduction in intraoperative frozen sections on positive margin findings in the final pathology report.

e12621 Background: In October 2023, intraoperative frozen section (IOFS) was restricted to breast cancer patients after neoadjuvant chemotherapy (NACT) only due to shortage of pathologists at the largest tertiary center in Austria. Here, we investigate the impact of the omission of IOFS on positive margins in the final pathology report. Methods: In this retrospective analysis, breast cancer patients undergoing breast conserving surgery at the University Hospital of Vienna between April 2020 and October 2024 were included. Patients after NACT, those who underwent mastectomy, had skin and/or muscle infiltration or other locally advanced disease were excluded from this analysis. Results: A total of 697 patients, 382 with IOFS before October 2023 and 315 without IOFS thereafter, with a median age of 63 years have been included in this analysis. No differences between IOFS and no-IOFS group were seen regarding median BMI (25.3 vs 25.6 kg/m 2 ), median tumor size (12mm vs 13mm; 1 to 75mm), multifocal disease (39pts (10.2%) vs 34pts (10.8%)), receptor status and grading as well as use of sentinel node removal (340pts (89%) vs 271 (86%)). Intraoperative re-excisions due to frozen resection result or gut feeling of the surgeon differed significantly (145 (38%) in the IOFS vs 41 (13%) in the no-IOFS, p < 0.001) with no difference regarding detection of residual cancer in those specimens (65 (44.8%) vs 16 (39%),p = 0.66). The final pathology result reported a significantly higher rate of positive margins in the no-IOFS group versus the IOFS group (94pts (29.8%) vs 82pts (21.5%), p = 0.011). This could be confirmed in the univariate logistic regression model (OR 1.56, CI1.11-2.2, p = 0.011) and was even more pronounced in the full multivariable logistic regression model (OR 2.06, CI1.36-3.14, p < 0.001) as well as in the final model after backward stepwise model selection based on AIC (OR 2.05, CI1.38-3.09, p < 0.001). Other factors that significantly impacted positive margins in the multivariate regression model were the presence of additional DCIS (OR 2.27, CI1.42-3.67, p < 0.001), lobular cancer (OR 3.29, CI1.56-6.85, p < 0.001) and multifocal disease (OR 3.22, CI1.86-5.58, p < 0.001). Of 610 patients, who underwent sentinel node removal 55pts (16.2%) had a positive SLN in the IOFS and 36pts (13.3%) in the no-IOFS group, respectively (p = 0.2). Conclusions: The cut down on intraoperative frozen section in a tertiary center led to a significant short-term increase in positive margins resulting in 30% of patients in the final pathology report with a doubling in the likelihood when compared to the use of IOFS. This may result in major increase in direct as well as indirect re-operation costs and psychological distress of the patients. Further follow-up is needed to analyze long-term effects of omitting IOFS on oncological outcomes.