Abstract PO3-17-01: Brazilian Real-world data of HR+ HER2- early-stage Breast Cancer (BC) patients are poor when compared to control arms of recent adjuvant clinical trials

Abstract INTRODUCTION: In Brazil, BC is the most common neoplasm among women, with 73k new cases annually. Adjuvant hormone therapy (HT) options are evolving with personalized strategies based on risk stratification. Real-world data (RWD) plays a crucial role in understanding the outcomes in BC patients (pts) in low- and middle-income countries, where significant health disparities, access gaps, and barriers to the implementation of guidelines exist. This study aims to assess the epidemiologic profile, practice patterns, and real-world outcomes of pts with ER+ HER2- stage I-III BC treated in the largest network of private oncology services in Brazil and compare results with control arms of recent clinical trials evaluating CDK4/6 inhibitors in adjuvant setting. METHODS: Retrospective RWD study from Oncoclínicas Group with longitudinal EHR data from 2017 to 2022 merged in a platform where structured variables (demographics, tumor staging, pharmacy records) are integrated with unstructured data from physician notes and digitized pathology-molecular reports using technology-based abstraction performed by expert human curators that follow mCODE standards and predefined ontology. Treatment patterns and invasive disease-free survival (IDFS) outcomes were collected. Regarding risk stratification, pts were classified as high-risk (HR) if: (i) 4+ axillary lymph nodes (LN), or (ii) 1-3 LN and grade 3 and/or Ki620% and/or high-risk ODX/Mammaprint; intermediate-risk (IR) if: (iii) 1-3 LN with grade 1-2 and/or Ki67 20% and/or non-high-risk ODX/Mammaprint, or (iv) N0 with grade 2-3 and/or Ki67 20% and/or high-risk ODX/Mammaprint; and low-risk (LR) if: (v) all other stages I and IIA not having the risk factors above. RESULTS: From over 30k BC pts in Oncoclínicas Database, 19k had HR+/HER2- early BC, 12k were treated in high-volume clinics, and 1,786 cases were selected for the study (diagnosis and first treatment in the last 6 years, complete histopathology and pharmacy registries). The median age was 57 years (27-96), 566 (32%) pts were premenopausal, 1052 (59%) had stage I disease, 372 (21%) stage IIA, 165 (9%) stage IIB and 197 (11%) stage III BC. Regarding risk stratification, 1,179 (66%) were LR, 351 (20%) IR, and 256 (14%) HR. In post-menopausal pts, aromatase inhibitor (AI) was used by 74% of pts with LR, 79% with IR and 83% with HR. In premenopausal pts, ovarian function suppression (OFS) – combined with tamoxifen or AI – was prescribed to 18% of LR pts, 15% of IR pts, and 48% of HR pts. Chemotherapy (CT) was offered to 32%, 38%, and 73% of postmenopausal pts in LR, IR, and HR groups. In premenopausal pts, 55%, 57%, and 78% received CT in LR, IR, and HR groups. The 3-year iDFS in the general population was 85%, reaching 80% in premenopausal and 86% in postmenopausal pts. The overall 3y iDFS was 87% in the LR, 86% in IR, and 72% in HR. Among premenopausal pts, the 3y iDFS was 81% in LR, 92% in IR, and 64% in the HR group. While the risk distribution of our cohort is similar to recent clinical trials, the 3y iDFS outcomes were numerically lower to those observed in the control groups of the pivotal trials evaluating adjuvant CDK4/6 inhibitors. In the HR group, the 3y iDFS was 72% (versus 84% 3y iDFS in the control arm of the MonarchE trial). Combining the IR/HR groups, the 3y iDFS was 80% (versus 87% in the control arm of NATALEE trial). CONCLUSION: In this large RWD cohort treated in a private setting in Brazil, most pts are diagnosed with stage I and LR BC. In this cohort, a significant proportion of premenopausal pts with IR/HR are not treated with OFS and do not receive CT. Real-world survival outcomes of Brazilian women with HR+ HER2- early BC treated in private clinic are inferior to those observed in recent clinical trials, especially in the premenopausal pts. In public healthcare system, where prevalence of HR disease is higher and access to essential treatments more limited, outcomes might even be worsened compared to the ones presented here. Citation Format: Aline Goncalves, Tomas Reinert, Max S. Mano, Heloisa Cruz, Cristiano Resende, Gustavo Bretas, Carlos Barrios, Matheus Costa e Silva, Rafael Paes, Guilherme Silva, Erika Martins, Fernanda Koyama, Bruno Ferrari, Carlos Gil Ferreira, Pedro Aguiar Junior, Rodrigo Dienstmann. Brazilian Real-world data of HR+ HER2- early-stage Breast Cancer (BC) patients are poor when compared to control arms of recent adjuvant clinical trials 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 PO3-17-01.