Male breast cancer is similar to breast cancer in females in its etiology, family history, prognosis, and treatment. In approximately 30% of cases of breast cancer in men, the family history is positive for the disease. A familial form of breast cancer is seen in which both genders are at increased risk for breast cancer. Male breast neoplasms are relatively rare, in contrast to gynecomastia, which is a relatively common condition. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
Male breast cancer accounts for less than 1% of all breast cancers diagnosed, with approximately 2600 cases annually in the United States, [12, 13, 14, 15] but the case fatality rate is similar to that in women.  The incidence of male breast cancer peaks at age 71 years. 
Risk factors for male breast cancer include BRCA mutation, estrogen exposure/androgen insufficiency (Klinefelter syndrome, obesity, cirrhosis, exogenous estrogen therapy, testicular abnormality), and radiation exposure. [16, 18]
Male breast cancer is most commonly invasive ductal or ductal carcinoma in situ (DCIS).  Male breasts lack terminal ductal lobular units, thus lobular carcinoma is extremely rare except in cases of estrogen exposure.
The majority of male breast cancers are estrogen and progesterone receptor positive, like in female breast cancer. However, male breast cancer is 3 times less likely to be HER2 positive. 
According to the American College of Radiology Appropriateness Criteria, for men younger than 25 years with an indeterminate palpable mass, ultrasound should be the first imaging modality used, because breast cancer is highly unlikely. Mammography should be performed if ultrasound findings are suspicious. For men who are 25 years or older or have a highly concerning physical examination, usually begin with mammography, and then ultrasound is useful if mammography is inconclusive or suspicious.