Abstract PS5-05-11: Real-world evaluation of treatment trends in breast cancer: the PRISMA study

Abstract Background: Breast cancer (BC) is the most common cancer and the leading cause of cancer-related death in women. Triple-negative BC (TNBC) and high-risk ER+ HER2- BC are aggressive BC subtypes with high recurrence rates. In Portugal, data on treatment of TNBC and high-risk ER+HER2- BC is limited. To address this, the PRISMA study collected quantitative data on treatment patterns and pathological complete response (pCR) from multiple Portuguese centers. Methods: Retrospective aggregated data from patients diagnosed between Jan-2019 and Jun-2023 were collected. The study included adult patients diagnosed with stage II - III TNBC or high-risk ER+ HER2- BC eligible for neoadjuvant (NAT) chemotherapy. Results: The study included 1585 patients, 642 (40%) with TNBC and 943 (60 %) with high-risk ER+HER2- BC. Most patients were ≥65 years with 1% being male. In both cohorts, most were diagnosed with stage II and were postmenopausal (62% and 73% in TNBC; 42% and 53% in ER+HER2-, respectively). Carcinoma of no special type was the predominant histology (88% TNBC and 83% ER+HER2- BC). In TNBC patients, the mean time between therapeutic decision and treatment initiation was five weeks (1 to 29 weeks), and from NAT completion to surgery was six weeks (3 to 8 weeks). Most TNBC patients underwent NAT chemotherapy (93%), primarily with carboplatin/paclitaxel and cyclophosphamide/doxorubicin or epirubicin (48%), resulting in a pCR rate of 47%. Surgery was performed in 99% of patients, with 59% undergoing conservative surgery. Adjuvant (AT) chemotherapy was given to 31% of patients, mostly with capecitabine (77%). Radiotherapy (RT) was performed in 72% of patients, primarily (66%) after conservative surgery, using conventional fractionation (50Gy/25fr, 48%). Among high-risk ER+HER2- BC patients, 81% cancers had Ki-67 ≥20%, and multi-gene assays were performed in 6%. 82% of high-risk ER+/HER2- patients underwent NAT and achieved a pCR of 9%. Dose dense AC or EC plus weekly paclitaxel was the most commonly used regimen (51%). The mean interval between NAT completion and surgery was 8 weeks (3 to 23 weeks). 59% of 939 patients undergoing surgery underwent breast conserving surgery. AT chemotherapy was administered to 18%, mostly with dose dense AC or EC and paclitaxel weekly (28%). RT was performed in 90% of patients, and 55% receiving it after conservative surgery. Regarding endocrine therapy (ET), 85% underwent adjuvant ET, with 68% using aromatase inhibitors. Ovarian suppression was performed in 26% of patients, frequently using gonadotropin-releasing hormone inhibitors (87%). Conclusions: The data provides a real-world characterization of TNBC and high-risk ER+HER2- BC treatment, demonstrating a high adherence to NAT chemotherapy and adjuvant ET, per guidelines, in this period. Observed delays in surgery suggest inter-hospital care variations that may inform healthcare policy, ultimately improving patient outcomes. Citation Format: G. Sousa, A. M. Ferreira, I. Pereira, A. Catarina, D. Simão, F. Machado, G. Fernandes, L. A. Ribeiro, J. Fougo, M. C. Nogueira, P. H. Meireles, J. Abreu Sousa, P. Cortes. Real-world evaluation of treatment trends in breast cancer: the PRISMA 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 PS5-05-11.