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 and 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 4366 BC patients received NACT, of whom 2008 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, 1749/2358 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.