Abstract PO1-22-09: Current margin assessment practice for breast-conserving surgery in China: a single institution audit

Abstract Background The appropriate negative margin width following breast-conserving surgery (BCS) for both ductal carcinoma in situ (DCIS) and invasive carcinoma (IC) has witnessed a shift towards de-escalation in international guidelines. However, there are limited nationwide data regarding margin assessment practice for BCS in China. This study aims to clarify the current real-world status of margin assessment from a single institution audit and secondarily to update the evidence on the association between margin width and local recurrence. Methods Eligible cases were derived from an extensive series of consecutive unselected patients with early invasive breast cancer who were treated with BCS at the Department of Breast Surgery in Shanghai Cancer Center Fudan University (FUSCC) between January 2015 and December 2017. Patient demographic and clinicopathological information as well as follow-up data were extracted from the hospital's electronic medical records. Pathological evaluation of negative margins was defined as no ink on tumor for IC in accordance with the SSO/ASTRO consensus guidelines released in 2014. Where applicable, margins were categorized as tumor on ink (involved), close margins (no tumor on ink but ≤1 mm), clear margins (1-2 mm), wide margins (2-5 mm), and wider margins (5 mm). The positive margin rate (PMR), reoperation rate, and ipsilateral breast recurrence (IBR) rate were calculated according to different margin widths. Multivariable analyses of factors associated with re-excision were performed using binary logistic regression. Kaplan‒Meier survival curve analysis was performed for local recurrence-free survival (LRFS). Results A total of 2707 patients were enrolled in the current study, with a total PMR of 2.7%. The distribution of margin width revealed that wider margins (5 mm) were optimized by most surgical oncologists (2092/2707, 77.3%) for BCS in our center. Additionally, the reoperation rates were 1.9% in the whole population, accounting for 48.3%, 7.5%, 4.2%, 0.8%, and 0.4% in each margin group. Specifically, among 247 patients with margins ≤2 mm, 41 (16.6%) received reoperation either by margin re-excision or mastectomy. Multivariable analyses identified that lobular histology, no selective additional resection and in situ pathology of involved/close margins are independent factors of re-excision recommendation. With a median follow-up of 54.3 months, the incidence of IBR was 1.7% in the whole cohort, representing for 5.2%, 4.2%, 2.8%, 1.9%, and 1.3% in each margin group, respectively. Kaplan‒Meier survival curve analysis showed a marginally significant difference in 5-year LRFS between groups with margins 2 mm and margins ≤2 mm (95.9% vs 97.8%, Table 1). Conclusions A wider margin width was preferably adopted in the routine practice of BCS. Our audit was aligned with previous evidence that a minimum clear margin of 2 mm is associated with a lower reoperation rate but favorable local control. Patients with margins no more than 2 mm were more likely to have re-excision in cases of lobular histology, no selective additional resection, and in situ pathology of involved/close margins. Ipsilateral breast recurrence models by margin status Citation Format: Feilin Qu, Cheng-Jia Shen, Wen-Tao Yang, Jun-Jie Li, Guangyu Liu, Zhi-Ming Shao. Current margin assessment practice for breast-conserving surgery in China: a single institution audit abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-22-09.