Abstract P4-09-13: Intraoperative assessment of margins in breast conserving therapy: Comparison of intraoperative specimen mammography and intraoperative pathologic evaluation

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Abstract Background: Breast-conserving therapy is a long-standing standard surgical procedure for treating breast cancer. The aim is the complete resection of the tumor with free margins to avoid additional surgery and possible relapse. The optimal way to document tumor-free margins intraoperatively is still unclear. Methods: In a retrospective study, we analyzed patients who underwent breast-conserving surgery for the treatment of early breast cancer in our institution. Patients with ductal carcinoma in situ (DCIS), locoregional relapse and those after neoadjuvant chemotherapy were excluded. We investigated the value of intraoperative pathologic evaluation compared with intraoperative specimen mammography for the assessment of tumor-free margins in breast conserving surgery. Results: Between 2009-2022, 465 patients underwent breast conserving surgery and received both intraoperative pathologic evaluation by frozen section and specimen mammography at our institution. The median age of the patients was 62 years. We found 59.1 % of the patients to have an invasive tumor not otherwise specified (NOS), 14.2% to present with an invasive lobular cancer and 18.1% with a mixture of both types, while 8.6% of our patients had another type of tumor, e.g. medullar. Most of the patients, 76.3 %, were node negative and had a tumor stage pT1c. The highest accordance between the results for frozen section and specimen mammography was seen in patients older than 70 years (77.7%), having an invasive breast cancer of no special type (73.8%) and a pT2 tumor stage according to the TNM classification (73.1%). Patients with a hormone-receptor negative tumor had higher accordance rates as well as those with a HER2 positive breast cancer. The difference between the accordance of the two methods was statistically significant only for patients younger than 50 years and those having a G3 tumor. To evaluate the value of the two methods for determining the margin during surgery we calculated the sensitivity, the specificity and the positive predictive value for the specimen radiography as compared to the frozen section resulting in 52.6%, 76.7% and 31.3%, respectively. Conclusion: The intraoperative specimen mammography is not a reliable method to assure tumor free margin for patients undergoing breast conserving surgery. The pathological evaluation of tumor specimen in addition to the specimen mammography resulted in a very low re-excision rate. Only 2.4% of the patients in our cohort had positive margins after complete pathological evaluation postoperatively. While the intraoperative frozen section seems to be the best way to avoid a second surgery, this method is costly and requires the presence of a pathologist. Thus, an improvement of the specimen mammography and the development of new imaging methods are needed. Citation Format: Susanne Briest, Alma Luise Bayer, Laura Weydandt, Mireille Martin, Anne Kathrin Höhn, Ivonne Nel, Bahriye Aktas. Intraoperative assessment of margins in breast conserving therapy: Comparison of intraoperative specimen mammography and intraoperative pathologic evaluation [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P4-09-13.

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