Abstract PO2-16-12: Real world evidence of neoadjuvant chemotherapy for breast cancer treatment in a Brazilian multicenter cohort: correlation of pathological complete response and overall survival

Abstract Introduction: Breast cancer is the most common malignancy among women in Brazil and worldwide. Neoadjuvant chemotherapy (NAC) has been increasingly used for the treatment of breast cancer conditions ranging from locally advanced tumors to early-stage triple-negative and HER-2 positive tumors. Nowadays only 5% of breast cancer patients are enrolled in clinical trials. Real-world data is important to evaluate how clinical trial treatments behave in the real world with all the heterogeneous patient characteristics of those treated differently from the homogeneity of clinical trials. Objectives: To evaluate the rates of pathological complete response (pCR) in patients undergoing neoadjuvant chemotherapy (NAC) for the treatment of breast cancer (BC) To examine the differences in pathological complete response (pCR) rates between HER-2 positive breast cancer patients with and without trastuzumab treatment, and between triple-negative breast cancer (TNBC) patients with and without platinum-based treatment, Additionally, we aim to assess the impact of pCR on overall survival (OS) and disease-free survival (DFS) using real-world data (RWD). Methods: This was a retrospective, multicentric cohort study, that included female patients over 18 years of age, with a diagnosis of non-metastatic breast cancer undergoing NAC. As an exploratory real-world data study, no confirmatory hypothesis was established, so no corrections for multiple comparisons were necessary. Overall survival (OS) and disease-free survival (DFS) were estimated by the Kaplan-Meier method calculated at five years. Additionally, we conducted a multivariate analysis to identify significant associations with pathologic complete response (pCR) and overall survival (OS). We employed a forest plot to visually represent these associations Results: From 2011 to 2020, 1,891 patients were included in the study, and 421 (22,3%) achieved pCR (ypT0 ypN0) and considering the presence of residual in situ carcinoma (DCIS) the pCR was seen in 467 patients (23,5) without significant difference (p=0,567) . The pCR rate varied between the subtypes: luminal A 17,0%, luminal B 21,3%, luminal HER2 23,0%, TNBC 22,5% and HER2 28,5% (p = 0,057). The type of neoadjuvant chemotherapy (NAC) regimen was correlated with pathological complete response (pCR). Among HER2-positive patients, those who received Trastuzumab had a significantly higher rate of pCR compared to those who did not receive it (p 0.0001). Similarly, in patients with TNBC, those who underwent treatment with platinum-based regimens also showed higher rates of pCR (p 0.0001). There were 694 deaths, and the 5-year OS rate was 62.9%. OS was also grouped according to pCR status, and pCR OS rate was 88,3% and non-pCR 58.1% significant difference observed (p 0.0001). Five-year DFS of pCR was 92.2% and non-pCR 64.3% (p 0.0001). Conclusion: this real-world data study evaluated the rates of pathological complete response (pCR) in breast cancer patients undergoing neoadjuvant chemotherapy (NAC). The results revealed varying pCR rates among different breast cancer subtypes, with HER2-positive and triple-negative subtypes showing higher rates. The use of Trastuzumab in HER2-positive patients and platinum-based regimens in triple-negative patients correlated with significantly higher pCR rates. Furthermore, achieving pCR was associated with improved overall survival (OS) and disease-free survival (DFS). These findings emphasize the importance of considering individual tumor characteristics and tailoring treatment strategies for breast cancer patients to optimize outcomes. Clinicopathological characteristics of patients AJCC, American Joint Committee on Cancer; IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; TNBC triple negative breast cancer. NAC schemas and correlation with pCR. AC-T, doxorubicin + cyclophosphamide – taxane; AC-TPlatinum, doxorubicin + cyclophosphamide – taxane+carboplatin; AC-TH, doxorubicin + cyclophosphamide – taxane+herceptin. Citation Format: Marcelo Antonini, Andre Mattar, Fernanda Grace Bauk Richter, Gabriel Pannain, Andressa Amorim, Marina Diogenes, Odair Ferraro, Luiz Gebrim, Reginaldo Coelho Lopes, Juliana Real. Real world evidence of neoadjuvant chemotherapy for breast cancer treatment in a Brazilian multicenter cohort: correlation of pathological complete response and overall survival abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-16-12.