Male breast cancer is a rare malignant tumor of breast tissue affecting male patients. Male breast cancer accounts for < 0.5% of all cancers diagnosed in men and for 1% of all breast cancers in the United States annually. Its incidence increases with age. Risk factors include family history, African descent, increased estrogen levels, gynecomastia, obesity, hepatic dysfunction, radiation exposure, Klinefelter syndrome, testicular disorders, and genetic mutations including BRCA1, BRCA2, CHEK2, and PALB2. However, it should be noted that most men with breast cancer have no identifiable risk factors.

Due to lack of awareness, patients may present at an advanced stage with a unilateral painless breast mass, nipple retraction, redness or scaling of the nipple, and axillary lymphadenopathy. The most common male breast cancer is due to invasive ductal carcinoma. Breast cancers in men are also more likely to be positive for estrogen receptor and negative for human epidermal growth factor receptor 2 (HER2).

Diagnostic tests include breast examination, mammography, and biopsy. Treatment is dependent on stage of disease and typically includes removal of breast tissue, radiation therapy, chemotherapy, and hormonal therapy.