Abstract PS2-03-09: Is it safe to offer breast-conserving surgery after neoadjuvant chemotherapy? A Brazilian multicenter cohort study

Abstract Background: Neoadjuvant chemotherapy (NAC) has become a cornerstone in breast cancer treatment, especially for locally advanced tumors and aggressive subtypes such as triple-negative and HER2-positive disease. NAC can reduce tumor size, increase breast-conserving surgery (BCS) eligibility, improve cosmetic outcomes, and allow early systemic control. However, concerns persist regarding whether BCS following NAC achieves oncologic outcomes comparable to those of BCS followed by adjuvant chemotherapy (AC). This study aimed to compare long-term survival outcomes in patients undergoing BCS after NAC versus AC in a real-world Brazilian cohort. Methods: We conducted a retrospective, multicenter cohort study across six Brazilian institutions (five private, one public). Women aged 18 years or older with clinical stage 0-III breast cancer who underwent BCS (either standard lumpectomy or therapeutic mammoplasty) between 2016 and 2022 were included. Patients were divided into two groups according to whether they received NAC or AC. Data on demographics, tumor characteristics, and treatments were collected from institutional registries. The outcomes assessed were locoregional recurrence-free survival (LRRFS), distant recurrence-free survival (DRFS), breast cancer-specific survival (BCSS), progression-free survival (PFS), and overall survival (OS). Survival outcomes were estimated using Kaplan-Meier methods, and Cox proportional hazards models were used to assess hazard ratios (HRs) and 95% confidence intervals (CIs). This study was approved by the IDOR Ethics Committee (reference 6,907,736). Results: A total of 268 women underwent breast-conserving surgery; 138 (51.5%) received NAC and 130 (48.5%) received AC. The mean age of the cohort was 53.1 years (SD 12.1), with patients in the NAC group being slightly younger (mean 51.1 vs. 55.2 years). Over half of the patients (56.8%) were over 50 years old, and 51.1% identified as white. Invasive ductal carcinoma was the predominant histological type (84.7%), and the majority of patients (73.8%) presented with early-stage disease (≤ stage IIA). Most underwent lumpectomy (72.4%), while 27.6% had therapeutic mammoplasty. In the NAC group, 57.2% had tumors classified as stage >IIB. After a median follow-up of 60 months, no statistically significant differences were observed in survival outcomes between the NAC and AC groups. The hazard ratio for LRRFS was 1.29 (95% CI: 0.28-5.88; p=0.816), for BCSS was 0.52 (95% CI: 0.10-2.61; p=0.473), for DRFS was 1.05 (95% CI: 0.31-3.52; p=0.955), for PFS was 1.19 (95% CI: 0.36-3.96; p=0.869), and for OS was 0.73 (95% CI: 0.18-2.91; p=0.710). Conclusion: In this multicenter Brazilian cohort, breast-conserving surgery following neoadjuvant chemotherapy was associated with survival outcomes comparable to those of surgery followed by adjuvant chemotherapy. These findings support the oncologic safety of BCS after NAC and reinforce its role as a safe and effective option in the individualized surgical management of breast cancer. Citation Format: A. Dominique Nascimento Lima, A. Mattar, F. Pimentel Cavalcante, F. Pereira Zerwes, M. Antonini, M. Leite Kraft, A. Oliveira de Alencar, A. de Queiroz Germano, D. Pitanga Torres, E. Goulart Carneiro, C. Freitas de Lima, R. Zocchio Torresan, F. Palermo Brenelli, M. Lichtenfels, A. Frasson, J. Bines, E. Camargo Millen. Is it safe to offer breast-conserving surgery after neoadjuvant chemotherapy? A Brazilian multicenter cohort study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-03-09.