Omitting re-excision for focally positive margins after breast-conserving surgery does not impair disease-free and overall survival

PURPOSE: In contrast to other countries, the Dutch breast cancer guideline does not recommend re-excision for focally positive margins after breast-conserving surgery (BCS) in invasive tumor and does recommend whole-breast irradiation including boost. We investigated whether omitting re-excision as compared to performing re-excision affects prognosis with a retrospective population-based cohort study. METHODS: The total cohort included 32,119 women with primary BCS for T1–T3 breast cancer diagnosed between 2003 and 2008 from the nationwide Netherlands cancer registry. The subcohort included 10,433 patients in whom the resection margins were registered. Outcome measures were 5-year ipsilateral breast tumor recurrence (IBTR) rate, 5-year disease-free survival (DFS) rate, and 10-year overall survival (OS) rate. RESULTS: In the total cohort, 25,878 (80.6%) did not have re-excision, 2368 (7.4%) had re-excision by BCS, and 3873 (12.1%) had re-excision by mastectomy. Five-year IBTR rates were 2.1, 2.8, and 2.9%, respectively (p = 0.001). In the subcohort, 7820 (75.0%) had negative margins without re-excision, 492 (4.7%) had focally positive margins without re-excision, 586 (5.6%) had focally positive margins and underwent re-excision, and 1535 (14.7%) had extensively positive margins and underwent re-excision. Five-year IBTR rate was 2.3, 2.9, 1.1, and 2.9%, respectively (p = 0.099). Compared to omitting re-excision, performing re-excision for focally positive margins was associated with lower risk of IBTR (adjusted HR 0.30, 95% CI 0.11–0.82), but not with DFS (adjusted HR 0.83 95% CI 0.59–1.17) nor with OS (adjusted HR 1.17 95% CI 0.87–1.59). CONCLUSION: Omitting re-excision in breast cancer patients for focally positive margins after BCS does not impair DFS and OS, provided that whole-breast irradiation including boost is given. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10549-017-4232-6) contains supplementary material, which is available to authorized users.