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Males infrequently develop breast cancer; hence the dearth of prospective randomized trials in male breast cancer. Our knowledge of the disease has been derived mostly from retrospectives studies. Due to the similarities of disease behavior in men and women with breast cancer, the management and treatment of male breast cancer has been guided by conclusions drawn from studies conducted in women.

Breast cancer represents less than 1% of all cancers in men1; the male to female ratio is 1:100.2 Since 1973 there has been a gradual increase in the incidence of male breast cancer, the reasons for which are unclear. Nonetheless the overall incidence remains low, at about 1 case per 100,000 population per year.3 Unlike women, where breast cancer displays a bimodal distribution, the disease in men increases exponentially with age. The median age at presentation for male breast cancer is 65 to 71, unlike with women, in whom breast cancer is seen about 5 to 10 years earlier.4 The epidemiology of breast cancer in men is similar to that in women, such that North America and Europe see the highest incidences, while Japan has the lowest.5 Interestingly, in sub-Saharan countries in Africa where infectious liver damage is common, such as in Zambia6 and Uganda,7 7% to 14% of breast cancer cases occur in men. In the United States, tumor registries indicate that male breast cancer is most common in African American men, intermediate in non-Hispanic Caucasian men and Asian-Pacific Islanders, and lowest in Hispanic men. In 2009, the American Cancer Society estimated that 1910 men will have been diagnosed with breast cancer in the United States, with 440 deaths.8

Similarly to women, hormonal factors seem to play an important role in the development of breast cancer in men. A frequently cited risk factor is Klinefelter syndrome, where an extra X chromosome is inherited in these male patients. The risk of developing breast cancer in patients with Klinefelter syndrome is increased by 58-fold, with an absolute risk of 3%.9 Patients with this syndrome have atrophic testes with high levels of gonadotropins, low levels of testosterone, and normal to low levels of estrogen, leading to a high estrogen to testosterone ratio. Also suggestive that hormonal factors may play a role, male breast cancer is seen in hermaphrodites, men having undergone feminizing surgery, and men who have received exogenous estrogen for prostate cancer, where cases of bilateral breast cancer have been described.10,11 As Klinefelter syndrome and male breast cancer are both rare diseases, it is very unlikely that a health care provider will encounter this situation; however, a breast lesion in a patient with Klinefelter syndrome must be considered suspiciously. It has been reported that 4% of men with breast cancer have Klinefelter syndrome.12

It has been suggested that male breast cancer and gynecomastia represent different ends of the same spectrum, or that gynecomastia may ...

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