Resection extent and clinical outcomes in breast-conserving surgery after neoadjuvant chemotherapy: a retrospective single-institution study

The optimal extent of resection in breast-conserving surgery (BCS) after neoadjuvant chemotherapy (NAC) remains controversial. This study descriptively evaluated the relationship between pre-NAC tumor extent, surgical specimen size, and clinical outcomes in patients undergoing BCS after NAC using a residual lesion-oriented surgical approach in routine clinical practice. We retrospectively reviewed 71 patients who underwent BCS after NAC between 2017 and 2020. The maximum tumor diameter on pre-NAC magnetic resonance imaging (MRI) (A) and the maximum diameter of the resected specimen (B) were compared for exploratory assessment and categorized as A < B, A ≈ B (difference within 1 cm), or A > B. Surgical margin status and recurrence outcomes were assessed. Residual lesions after NAC were primarily localized using ultrasonography and MRI, with ultrasonography used for surgical planning immediately before surgery. The median age was 50 years, and 56.3% of tumors were HER2-positive. Pathological complete response was achieved in 57.7% of patients. Negative margins were obtained in 61 patients (85.9%), while 6 patients had positive margins and 1 patient had a close margin. The A < B group comprised 62 patients, the A ≈ B group 8 patients, and the A > B group 1 patient. During a median follow-up of 4.7 years, ipsilateral breast recurrence occurred in two patients (2.8%) and distant recurrence in three patients (4.2%). No apparent association between A/B classification and recurrence was observed; however, meaningful comparisons between groups were limited by the marked imbalance in group sizes and the small number of recurrence events. This study provides descriptive, real-world data on surgical specimen size and clinical outcomes in patients undergoing BCS after NAC using a residual lesion-oriented approach. Acceptable pathological margin status and favorable local control were observed in this single-institution cohort. However, the A/B comparison is a crude surrogate for the extent of tissue resection because specimen size was substantially influenced by the gross surgical margin, and the study was not designed to establish the oncological safety or equivalence of residual lesion-oriented resection compared with pre-treatment tumor footprint-based resection. Larger prospective multicenter studies incorporating standardized quantitative imaging assessment and direct comparison of surgical strategies are warranted to determine the optimal extent of resection and appropriate patient selection after NAC.