What are the Determinants of Type of Breast Surgery following Neoadjuvant Chemotherapy? An analysis of Breast Cancer Patients among Italian SENONET Centers: NEOIMPACT Study

Background Concerns remain regarding determinants of breast-conserving surgery (BCS) following NACT, particularly in presence of a pathologic complete response (pCR). Methods Retrospective analysis of 65,926 women treated at 26 Italian Breast Centers between 2017-2022 using the data-warehouse, SENONET. Clinical and pathological data of patients treated with NACT were analyzed to identify factors influencing surgical decision-making. Results A total of 4,366 BC patients received NACT, of whom 2,008 women (46%) underwent BCS. A non-significant trend over time in the adoption of BCS was observed (p=0.187). Lower rates of BCS were significantly associated with age ≤49 years, multifocal/multicentric disease, microcalcifications, presence of DCIS, tumor ≥2 cm or cN+ (p<0.05). A pCR was achieved in 31% of patients but was not associated with higher BCS rates (p=0.353). Among patients achieving a pCR with either unifocal or multicentric tumor, 283/783 (36%) and 104/117 (89%) women underwent mastectomy, respectively. After mastectomy, 1,749/2,358 patients (74%) received breast reconstruction, with an increase over time for both an immediate breast reconstruction (IBR) and a nipple-sparing mastectomy approach (p=0.012). Age <50 years and pCR were significantly associated with IBR (p<0.001) while cT2+ stage (p=0.028), cN+ (p<0.001), and age >70 years (p<0.001) resulted negatively associated with IBR. Conclusions BCS remains underutilized after NACT, and surgical choices continue to be predominantly guided by pre-treatment clinical features rather than tumor response. Even among patients with biologically responsive unicentric tumors and those achieving pCR a significant propensity for mastectomy persists. These findings highlight the urgent need for updated guidelines to reduce unnecessary mastectomies.