Cardiovascular versus breast cancer mortality in men with breast cancer: An age-stratified SEER competing-risk study.

Male breast cancer is rare and predominantly affects older patients, who face a substantial competing burden of cardiovascular disease. We aimed to characterize age-specific cumulative incidences of breast cancer, cardiovascular, and other-cause mortality and determine when cardiovascular cumulative incidence overtakes that of breast cancer. Using the Surveillance, Epidemiology, and End Results (SEER) database, we identified men diagnosed with non-metastatic invasive breast cancer during 2000-2022. Cause-specific cumulative incidence was estimated using the Aalen-Johansen estimator, with cardiovascular-breast cancer differences at 5 and 10 years as the primary comparison. Factors associated with cardiovascular death were evaluated using cause-specific Cox and complementary Fine-Gray models. Among 6702 men followed for a median of 67 months, 665 cardiovascular deaths occurred. Mortality patterns were strongly age-dependent. In men aged 80 years or older, cardiovascular cumulative incidence exceeded breast cancer cumulative incidence by 4.6 percentage points at 5 years and 14.6 percentage points at 10 years. In men aged 70-79 years, the differences were not significant at either time point, although an exploratory sustained crossover occurred near 13.6 years. After adjustment, age 80 years or older was strongly associated with cardiovascular death compared with age 60-69 years (hazard ratio 8.54, 95% confidence interval 6.89-10.60); regional stage and unmarried status were also associated with higher cardiovascular mortality. In men with non-metastatic breast cancer, cardiovascular cumulative incidence overtakes that of breast cancer early after diagnosis in the oldest patients. These findings support age-aware cardiovascular attention during survivorship but do not establish that intensified cardiovascular surveillance improves outcomes.