Male breast cancer is a rare disease and clinical or epidemiological data are available from only a relatively few cases. Nonetheless, both similarities and discrepancies are apparent between breast cancer in men and women. For example, lobular and mucinous carcinomas are seldom seen in men. Tumors in men more often display neuroendocrine differentiation, with an average age at diagnosis ten years later than in women. A high proportion of breast tumors in men are estrogen receptor-alpha positive (in this review 77%) and progesterone receptor positive (76%). Breast tumors in men often respond favorably to endocrine manipulation, including testicular ablation or antiestrogen therapy. Thus, the hormone receptors in these tumors can be functionally active and used for therapeutic intervention. This proposal has been questioned in some studies because estrogen dependent proteins are expressed to a lesser degree in men. Furthermore, men do not have a better overall breast cancer prognosis compared with women, after adjustments have been made for age and tumor stage. While the androgen receptor content has been assessed in a few studies, there are no studies on the estrogen receptor-beta content of breast tumors in men.