Abstract P2-10-11: Utilization and impact of endocrine therapy in male patients with early breast cancer – results from a large German real-world claims data analysis

Abstract Male breast cancer (BC) is a rare entity and presents a significant clinical challenge due to its late diagnosis and the resulting poorer prognosis compared to female BC. As shown by prior studies, approximately 99% of male BC patients are hormone receptor-positive (HR+). Given the lack of large prospective trials on optimal therapy of male BC, treatment is analogous to that of female BC. The objective of this study was to analyze the use of endocrine treatment (ET) in male patients with early BC using claims data from a large German health insurance provider (AOK Baden-Wuerttemberg) and to assess the impact of ET on overall survival (OS). Male patients who underwent surgery for early breast cancer between July 1st 2010 and December 31st 2019 were included into the analysis. As the data-set did not include information on the HR status, we assumed all patients to be HR+. Utilization of endocrine therapy was assessed based on filled prescriptions. Overall survival (OS) was defined as the period between first diagnosis of EBC until death. In total, 144 male BC patients were included, as well as 432 age-matched controls. 21/144 patients (15%) did never use any ET. Most of the patients who received ET (93/107) were treated with tamoxifen (87%). Patients, treated with ET showed the same nodal status (N0: 72/107, 67%; N+: 35/107, 33%) as compared to patients without ET use (N0: 18/21, 86%; 3/21, 14%, p=0.091). However, patients treated with ET as compared to patients without ET were more likely to receive radiation therapy (with ET: 61/107, 57%; without ET: 2/21, 10%; p < 0.001) and to receive chemotherapy (with ET:54/107, 50%; without ET:1/21 (5%), p < 0.001). 5-year OS of patients who never started with ET was significantly reduced compared to patients with ET (without ET 37 % (95 % CI: 20 – 69 %) vs. with ET 74 % (95 % CI: 64 – 84 %), p < 0.001). Multivariate cox regression including age, nodal involvement, use of radiation therapy, and chemotherapy use revealed that age and intake of ET were independent prognostic factors for OS. Although nearly all male breast cancer patients are HR+ a clinically relevant proportion never starts with ET. These patients have a significantly reduced OS as compared to patients who start with ET. Future research should focus on adherence to ET and factors that influence the utilization of ET. Citation Format: Dominik Dannehl, Tobias Engler, Tjeerd Dijkstra, Alexandra von Au, Lea Volmer, Markus Hahn, Sabine Hawighorst-Knapstein, Ariane Chaudhuri, Markus Wallwiener, Florin-Andrei Taran, Armin Bauer, Sara Brucker, Stephanie Wallwiener, Andreas Hartkopf. Utilization and impact of endocrine therapy in male patients with early breast cancer – results from a large German real-world claims data analysis [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-10-11.