Male breast cancer is rare. An estimated 1,990 new cases of breast cancer will be diagnosed in men in the U.S. during 2008. In 2004, the overall incidence of breast cancer in men was 1.4 per 100,000, compared to 124 per 100,000 in women. Differences in mortality were equally wide: 0.3 per 100,000 in men; 24 per 100,000 in women.
As with women, invasive ductal carcinoma accounts for most of the breast cancers seen in men, with ductal carcinoma in situ and invasive lobular carcinoma accounting for only a small proportion of cases.
The strongest risk factor for breast cancer among men is Klinefelter's syndrome, a condition associated with condition occurs when men are born with two X chromosomes (XXY instead of XY) [Although men with Klinefelter's syndrome may have gynecomastia (enlargement of the breast tissue), gynecomastia not associated with Klinefelter's syndrome does not appear to be related to breast cancer among men .[Similar to female breast cancer, male breast cancer risk is increased in men with a mutation in the BRCA2 gene .
Chronic alcoholism, chronic liver disease and obesity may also increase the risk of male breast cancer.