Abstract PS3-11-03: Pathologic Complete Response and Surgical Outcomes, in a Brazilian Cohort

Abstract Introduction: Neoadjuvant chemotherapy (NACT) is a treatment strategy for locally advanced tumors and even for operable tumors in situations that can determine prognosis, modify adjuvant treatment and reduce surgical intensity. Method: This study evaluated Brazilian patients undergoing NACT from 2013-2023 in a Cancer Center in Brazil, through a retrospective cohort, analyzing the chemotherapy (CT) performed, pathological complete response rate (pCR) and surgical outcomes, the latter particularly in the HER2 positive (+) and Triple Negative (TN) population. Results: A total of 1,626 female patients were included, median age at diagnosis 46. The most frequent tumor subtype was luminal B (38.4%), followed by Her2 + (29.5%, including luminal) and TN (27.4%). Locally advanced tumors (T3-T4) accounted for 53.5% of cases and 67.2% were cN+ (cN1- 45.2%, cN2 -16.1% and cN3- 5.9%). Of the breast surgeries, 33.9% were conservative (BCS), 61.4% mastectomies, 4.7% nipple-sparing. Of the axillary surgeries, 38.0% were sentinel lymph node biopsies (SLNB), 67.1% lymphadenectomies (LA). The pCR occurred in 38.3% of cases, but was higher depending on the treatment modality, as shown in the table 1. The high-volume disease also influenced the pCR: N1 (16.4%) compared to N3 (1.6%, p0.05). BCS were more frequent in the TN group than in the luminal group (11.7% vs. 0.4%; p0.05). In HER2+ sample, BSC was significantly higher (23.6%) in the group that received double target therapy (DTT) (trastuzumab only, 12.2%; p0.05) , as well more number of SLNB (27.6%/DTT group vs. 14.7%/trastuzumab group; p0.05). Of the total patients, 80.1% were alive without disease, 20.6% showed progression and 11.4% died of BC. Discussion: Achieving a pCR is one of the objectives of NACT, especially for TN/HER2 + tumors with an impact on survival (Cotazar P et al, 2014.) and on the definition of adjuvancy. In addition, another objective of NACT is to promote BCS, as seen in our series, which was also higher in the TN group than in the Luminal group. Mattar et al. evaluated patients treated with NACT in Brazil, and showed an overall pCR rate of 22.7%, lower than in this study (38.3%), probably due to the disparity in access between public and private treatments in the country. The pCR rate in this study was also higher than in other studies published in Latin America, such as the study by Acevedo F et al. and VillaReal Garza C et al., ranging from 24.1% to 28.1%. Anti-HER2 DTT started (2015), we observed in our series an absolute increase in pCR of 11%, and after the brazilian approval of pembrolizumab, an absolute increase of 8% in pCR of TN, a fact that contributes to the higher number of BCS. Conclusion: The reproduction of NACT regimens carried out in pivotal studies in the general population achieves comparable results in terms of pCR and contributes to promoting more BCS, especially in the TN/HER2 + group. Citation Format: M. Canal, R. Santos, S. Santos, M. Tavares, A. Bitencourt, M. Andrade, S. M. Sanches, F. Makdissi. Pathologic Complete Response and Surgical Outcomes, in a Brazilian Cohort 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 PS3-11-03.