Abstract PS3-08-20: Sex-based differences in hormone receptor-positive breast cancer treatment and outcomes: A Veterans Health Administration 20-year cohort study

Abstract Background: Estrogen receptor-positive (ER+) breast cancer is the most commonly diagnosed subtype in both male and female patients. However, due to the rarity of male breast cancer overall, there remains limited understanding of how this specific subtype is treated and how outcomes compare between sexes. This study aims to compare survival and contemporary treatment for ER+ male breast cancer (MBC) and female breast cancer (FBC) patients within the Veterans Health Administration (VHA). Methods: We conducted a retrospective cohort study of patients diagnosed with ER+ MBC and FBC between 2000 and 2020 using national data from the VHA Informatics and Computing Infrastructure database. Demographics, tumor characteristics, treatment (surgery, chemotherapy, radiation), and survival were compared between MBC and FBC patients. Stage 0 and IV patients were excluded from our analysis. Descriptive statistics, t-tests, and chi-square tests were used to compare the cohorts. Cox proportional hazards regression models were utilized to examine overall survival, controlling for age, race, body mass index, and grade. Results: Of the 6,336 total patients identified, 17.9% (n=1,134) were male. ER+ MBC patients were 66.0% White (n=754), 23.0% Black (n=257), and 11.0% Other/Unknown race (n=123). Most ER+ MBC patients were Non-Hispanic (n=1024, 90.0%). The average BMI of ER+ MBC patients was 30.6. ER+ MBC patients were significantly more likely to be diagnosed at an older age (69.0 vs. 57.7, p