Introduction/Background There is no evidence that resection margins after breast conserving surgery (BCS), defined as ’no ink on tumor’ can be applied to patients receiving neoadjuvant systemic treatment (NST). The study aim was to evaluate the impact of the distance of the resection margins on the loco-regional recurrence (LRR) and the survival of patients treated by BCS following NST.

Methodology This is a retrospective study including patients who underwent NST followed by BCS. The LRR-free survival (LRRS), disease-free survival (DFS) and overall survival (OS) was assessed according to the tumor margin distance status at final pathology. The Kaplan-Meier method was used to analyze survival and the Cox model was used to perform uni and multivariate analyzes.

Results A total of 235 patients were included in this study. Median tumor size at diagnosis was 30mm (7–75mm). A neoadjuvant chemotherapy was administrated to 91.5% patients. A complete response at imaging has been found in 27.3% of patients and 32.5% of them showed no residual tumor at final pathology. The final pathology found positive (’no ink on tumor’) margins in 8,9% patients and margins ≤1mm in 11.1% women. With a median follow-up of 63.4 months, there were 26 LRR. The 5 years LRRS was 88.7% in patients with negative margins and 87.3% in those with positive margins (p=0.7093). The surgical margins >1mm seem to be more benefic, with a LRRS at 91.5% comparing to those with margins ≤1mm (78.4%, p=0.0013). This surgical margin, >1mm, have been found to be significant for both DFS (p=0.0006) and OS (p=0.0013).

Conclusion The surgical margin distance >1mm seem to be the most appropriate surgical margin for breast cancer patients treated with BCS after NST. This margin >1mm could be useful to ameliorate the LRRS (p=0.0013), the DFS (p=0.0006) and OS (p=0.0013) of these group of breast cancer patients.

Disclosures None