Oncologic safety of breast conserving surgery after neoadjuvant chemotherapy in patients with multiple ipsilateral breast cancer: A retrospective multi-institutional cohort study

Introduction: The recent ACOSOG Z11102 trial demonstrated low recurrence rates with breast conserving surgery (BCS) in women with multiple ipsilateral breast cancers (MIBC). Questions remain regarding the oncologic safety of BCS in women with MIBC receiving neoadjuvant chemotherapy (NAC). Methods: We conducted a retrospective cohort study of adult patients who underwent BCS following NAC for stage I -III breast cancer from 2012 to 2021 at two academic centers. Descriptive statistics were used to summarize the data and the Kaplan -Meier method was used to provide estimates for recurrence and survival outcomes. MIBC was defined as >= 2 foci of malignancy. Results: A total of 544 patients were included; 29.4% (n = 160) ER+/HER2-, 17.7% (n = 96) ER+/HER2+, 18.2% (n = 99) ER-/HER2+, and 34.7% (n = 189) with ER-/HER2-disease. Overall, 80.5% (n = 438) had unifocal breast cancer while 19.5% (n = 106) had MIBC. Of patients with MIBC, 90.6% (n = 96) had multifocal and 9.4% (n = 10) had multicentric disease. Pathologic complete response was achieved in 41.1% of patients with MIBC versus 41.5% of patients with unifocal disease (p = 0.94). At a median follow-up of 55 months (IQR 32-83); 4.8% of patients in the unifocal group and 4.7% of patients in the MIBC group had had a local recurrence (p = 0.97). There was no difference in 5 -year local recurrence -free survival (p = 0.92), recurrence -free survival (p = 0.06), or overall survival (p = 0.07) between the groups. Conclusion: In this large cohort of women undergoing BCS post-NAC, there was no significant difference in in breast tumor recurrence or survival outcomes between patients with unifocal disease and those with MIBC.