Surgical Margin Width Does Not Impact Local Recurrence Across Tumor Subtypes After Neoadjuvant Systemic Treatment and Breast‐Conserving Surgery

INTRODUCTION: Neoadjuvant systemic treatment (NAST) is the standard of care for patients with large tumors and/or regional lymph node involvement, particularly in those with HER2-positive or triple-negative breast cancer. A key advantage of NAST is tumor downstaging, which facilitates breast-conserving surgery (BCS). However, the impact of surgical margin width on local recurrence rates across different tumor subtypes remains unclear. METHODS: breast cancer who received NAST followed by BCS and locoregional radiotherapy were included. Two comparisons were performed: (1) patients with IITR versus those without, to identify factors related to recurrence; and (2) patients within each tumor subtype, to examine IITR rates according to surgical margin width. RESULTS: Among 429 patients (median age 48 years; range, 26-75) with a median follow-up of 55 months (range, 4-199), IITR occurred in 16 patients (3.7%). IITR rates were similar across subtypes: 2.8% (n = 6) in HR+/HER2-, 6.3% (n = 5) in HR+/HER2+, 4.0% (n = 2) in HR-/HER2+, and 3.7% (n = 3) in triple-negative tumors. No significant difference in IITR rates was found when stratified by surgical margin width within each subtype. Younger patient age was the only factor significantly associated with IITR. Breast cancer-specific mortality was significantly higher among patients with HR-/HER2+ and triple-negative tumors compared with those with HR + tumors. CONCLUSION: IITR was infrequent among patients undergoing BCS after NAST. Minimal clear margins (no ink on tumor) were found to be safe across all tumor subtypes in cases without complete response to NAST. Younger age was independently associated with higher IITR risk, regardless of margin width or tumor subtype.