Breast cancer in men is a rare disease, accounting for approximately 1% of all 
breast cancer cases. Although the epidemiologic literature regarding female 
breast cancer is extensive, relatively little is known about the etiology of 
male breast cancer (MBC). This review is intended to summarize the existing body 
of evidence on genetic and epidemiologic risk factors for breast cancer in men. 
Overall, the epidemiology of MBC presents similarities with the epidemiology of 
female breast cancer. Major genetic factors associated with an increased risk of 
breast cancer for men include BRCA2 mutations, which are believed to account for 
the majority of inherited breast cancer in men, Klinefelter syndrome, and a 
positive family history. Suspected genetic factors include AR gene mutations, 
CYP17 polymorphism, Cowden syndrome, and CHEK2. Epidemiologic risk factors for 
MBC include disorders relating to hormonal imbalances, such as obesity, 
testicular disorders (e.g., cryptorchidism, mumps orchitis, and orchiectomy), 
and radiation exposure. Suspected epidemiologic risk factors include prostate 
cancer,prostate cancer treatment, gynecomastia, occupational exposures (e.g., 
electromagnetic fields, polycyclic aromatic hydrocarbons, and high 
temperatures), dietary factors (e.g., meat intake and fruit and vegetable 
consumption), and alcohol intake.