Factors Associated With Male Breast Cancer Incidence Among Prostate Cancer Survivors: Real World Evidence From Veterans Affairs National Prostate Cancer Data Core

Background While male breast cancer incidence is rare, veteran status is found to be associated with increased risk, for incidence, a higher prevalence of male breast cancer patients was observed among male veteran prostate cancer survivors. This study leveraged the existing large‐scale Veterans Affairs (VA) Prostate Cancer Data Core and examined factors associated with increased risk of male breast cancer incidence in veterans with prior prostate cancer diagnoses. Methods A retrospective cohort study of 1.3 million male veterans treated for prostate cancer at VA hospitals was conducted using the VA Prostate Cancer Data Core. Of these, 11,327 (0.86%) were newly diagnosed with male breast cancer on average 5.4 years post prostate cancer diagnosis. Results Multivariate Cox and competing risk model results found that younger onset age of prostate cancer (hazard ratio [HR] 0.97, 95% confidence interval [CI] 0.97–0.98), metastasized prostate cancer (HR 2.03, 95% CI 1.90–2.17), being Non‐Hispanic (N‐H) Black (HR 1.10, 95% CI: 1.05–1.15), radiation (HR 1.06, 95% CI: 1.02–1.11) and androgen deprivation therapy (ADT; HR 1.24, 95% CI 1.17–1.32) were associated with significantly increased risk of male breast cancer diagnosis. Prolonged use of cardiovascular disease (CVD) medications, furosemide (HR 1.51, 95% CI 1.39–1.63), spironolactone (HR 1.36; 95% CI 1.15–1.61), and digoxin (HR 1.50, 95% CI: 1.29–1.72), significantly increased risk for male breast cancer incidence. Conclusions Younger age onset of prostate cancer, metastasized prostate cancer, prolonged use of CVD medications, radiation, and ADT cancer treatment were factors significantly associated with increased risk of being diagnosed with male breast cancer among male veteran prostate cancer survivors. The study findings may shed insights in cardio‐oncology specific risk factors for male breast cancer among prostate cancer survivors.