Abstract PS3-09-26: Real-world clinical characteristics, treatment patterns and outcomes among UK and French patients with early-stage, estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer treated wi

Abstract Background: ER+/HER2-breast cancer (BC) is heterogeneous, with a subset of patients at high risk of recurrence and poorer outcomes. The treatment landscape for the high-risk group is evolving, with growing emphasis on survival benefits from adjuvant and neoadjuvant treatments. This study aimed to describe the real-world characteristics, treatment patterns, and outcomes for high-risk patients who received neoadjuvant chemotherapy (NACT). Methods: This was an observational, retrospective cohort study using electronic health records from five oncology centers across France and the UK. The study included patients with high-risk (grade III and clinical stage T1c-T2/N1-N2 or T3-T4/N0-N2), early-stage, ER+/HER2-BC initiating NACT (index date) between Jan 2013 and Dec 2020 (Jan 2014-Dec 2020 at one site). Patients participating in clinical trials were included. Demographics, prescribed treatments, and real-world pathological complete response (rwpCR) were detailed using descriptive statistics. Results: The study included 281 patients, 167 French (59.4%) and 114 British (40.6%). Patients were diagnosed with T1c-T2 and N1-N2 (157, 55.9%) or T3-T4 and N0-N2 (124, 44.1%) BC (including American Joint Committee on Cancer, version 7 stages II, IIA and IIB). At diagnosis, 235 patients (83.7%) were ER-positive (≥10% expression) and 84 (49.7%) of 169 patients with known status were post-menopausal women. Only 58 patients (20.6%) were tested for BRCA, with 11 (19.0%) positive. PD-L1 and prognostic genomic tests were rarely conducted. Of 229 patients with ECOG score at index, 207 (90.4%) had a 0 score. Prescribed agents are presented in the Table: 263 patients (93.6%) received NACT alone (i.e., without radiotherapy or other treatments). The most common (271 patients, 96.4%) NACT agents were anthracycline (A) with cyclophosphamide (C), mostly combined with a taxane (T; 257 patients, 91.5%). The most common reasons for NACT initiation (available for 92 patients) were clinical node involvement (46, 50.0%), large unifocal primary tumor (30, 32.6%), or multifocal disease (15, 16.3%). The median (Q1, Q3) duration of NACT was 4.4 (3.5, 4.8) months. At the time of surgery, rwpCR (ypT0/Tis ypN0) was achieved by 29 patients (10.3%). Overall, 221 patients (78.7%) were alive at the time of data provision (median follow up: 68.8 months). Conclusions: These initial results provide insights into the real-world characteristics and prescribed treatments of patients with stage II- III ER+/HER2- early BC initiating NACT. Treatment was primarily based on A, C and T. The recorded low rwpCR confirms the high unmet need for newer therapies in this setting. Further analyses will focus on treatment sequencing and real-world effectiveness. Citation Format: P. S. Hall, E. Sawyer, J. Frenel, K. Desai, K. M. Hirshfield, G. Gooud, D. Ntais, A. Jamotte, C. Perkins, A. Babonneau, E. Kitetere, M. Vallet, M. Riaz, J. Timbres, L. Haroun, L. Cirneanu, R. Hermans, V. Saglimbene, K. Dushkin, A. Ajmal, S. Oikonomou, A. Vladimirova, J. Earla, F. Bocquet, P. Cottu. Real-world clinical characteristics, treatment patterns and outcomes among UK and French patients with early-stage, estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer treated with neoadjuvant chemotherapy [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 PS3-09-26.