Abstract Background: Male breast cancer is rare and understudied,with most treatment paradigms based on evidence from females. Existing studies suggest that men may have lower adherence to hormonal therapy, but large-scale data are limited. Hormonal therapy adherence significantly impacts outcomes in breast cancer treatment. However, differences in adherence patterns between male and female veterans remain understudied. Understanding these patterns is crucial for developing targeted interventions to improve adherence and patient outcomes. Methods: We conducted a retrospective cohort study using national data from the Veterans Health Administration (VHA) Informatics and Computing Infrastructure database. Veterans diagnosed with breast cancer and prescribed adjuvant hormone therapy (tamoxifen,anastrozole, letrozole, or exemestane) between January 1, 2005, and December 31, 2019,were included. Demographic and clinical characteristics were collected, and adherence was assessed. Multivariable logistic regression was utilized to identify factors associated with adherence, comparing male and female veterans. Results: A total of 7,155 veterans (1,139 males and 6,016 females) were analyzed. Male veterans were older at initial prescription (69.8 ± 10.0 years vs. 58.2 ± 10.7 years for females, p0.001) and had higher adherence rates (74% vs. 65%, p0.001). Multivariable regression indicated that adherence significantly increased with older age (Adj. OR: 1.03, 95% CI: 1.02-1.03;p0.001) and among non-Hispanic/Latino individuals (Adj. OR: 1.39, 95% CI: 1.10-1.75;p=0.005), but decreased among Black veterans compared to White veterans (Adj. OR: 0.60,95% CI: 0.53-0.67; p0.001), divorced/separated individuals (Adj. OR: 0.86, 95% CI: 0.75-1.00; p=0.049), widowed individuals (Adj. OR: 0.76, 95% CI: 0.60-0.95; p=0.018), and those with unknown cancer stage (Adj. OR: 0.80, 95% CI: 0.65-0.98; p=0.030). After adjustment, gender alone was not predictive of adherence (Adj. OR: 1.02, 95% CI: 0.87-1.20; p=0.771). Importantly, adherence to hormone therapy was significantly associated with reduced mortality risk (Adj. OR: 0.76, 95% CI: 0.67-0.86; p0.001). Conclusion: Adherence to hormone therapy significantly improves survival outcomes among veterans with breast cancer. While male veterans demonstrated higher adherence rates, gender was not independently associated with adherence after adjustment. Targeted interventions addressing adherence disparities—particularly among younger, Black, divorced/widowed individuals,and patients with uncertain staging—could improve outcomes and reduce health disparities. Citation Format: S. Prasad, J. Gruber, R. Aft, A. Naaseh, M. Schoen. Comparative Adherence to Adjuvant Hormonal Therapy and Associated Mortality in Male and Female Veterans with Breast Cancer: A Nationwide Cohort Analysis 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 PS4-11-20.
Prasad et al. (Tue,) studied this question.