Many people are unaware that men can develop breast cancer too. Delay in diagnosis and presentation with advanced disease are common. Any breast lump, nipple discharge, or change in the breast should be investigated. Most of the breast tissue in a man is concentrated in the area immediately behind the nipple and areola. Androgen appears to suppress any tendency for ductal proliferation, but as men age and the overall level of androgen decreases, some physiologic enlargement of the breasts can occur. In most men this is of no concern. Because most of the breast tissue is beneath the nipple/areola complex, this is where most male breast cancer starts. There is a rich plexus of lymphatics beneath the nipple and areola in both men and women, and the subareolar location of most male breast cancers allows easy access of tumor cells to these lymph channels.
For every 100 women who develop breast cancer in the US, one male is diagnosed with the equivalent disease. The overall incidence is between 0.1 and 3.4 cases per 100,000 man-years. This makes male breast cancer one of the rarest malignancies, contributing to the generally low level of public awareness. While the average age at diagnosis is around 65 years, the problem can occur in younger (or older) men.
Men have glandular breast tissue that is subject to hormonal influences. Excess estrogen, especially around the time of puberty, has been identified as a possible factor. Men with Klinefelter's syndrome have an increased risk of developing breast cancer, as do men who take estrogens or estrogen-like compounds. Androgen (and possibly progesterone) exert a protective influence. Men who are deficient in androgen seem to also be an increased risk (for example, men who have testicular atrophy from mumps orchitis, injury, or undescended testes). Brain tumors and conditions associated with excess production of prolactin have also been implicated in some cases of male breast cancer.
Men who work in steel mills, blast furnaces, rolling mills, or other environments of intense heat have a slightly increased incidence of breast cancer (probably due to thermal suppression of androgen production). Radiation to the chest wall increases the risk of breast cancer in men, as in women. Finally, genetic factors have been identified in some cases of male breast cancer.
Nipple discharge, either bloody or serous, is distinctly abnormal in men and must always be taken seriously. Although it may very well turn out to be nothing, it should always be followed up with mammography and biopsy if any mammographic abnormality is found.
The chances of developing male breast cancer in both breasts simultaneously is extremely low.