Male breast cancer is a rare disease, accounting for less than 1 percent of all breast cancer cases. Because of the low incidence of this disease, its cause and pathogenesis are not completely understood. Men are not routinely screened for the disease and usually do not think about the possibility of acquiring it. As a result, breast cancer, when first detected in a man, tends to be more advanced than when it is first diagnosed in women.
Scientists have discovered congenital, biological, and environmental factors that can increase risk of breast cancer in men. Some of these are related to sex hormone levels in the body. Risk factors include:
* Obesity: Fat cells in the body convert male hormones into female hormones, so that obese men have higher levels of estrogens in their bodies.
* Alcohol: Heavy alcohol intake increases the risk because of its effects on the liver.
* Liver disease: The liver plays an important role in sex hormone metabolism by making binding proteins that carry the hormones in the blood. Men with severe liver disease have relatively low levels of androgens and higher estrogen levels.
* Estrogen treatment: Men who take high doses of estrogens as part of a sex-change procedure or who take estrogen-related drugs to slow the growth of prostate cancer have a higher risk of breast cancer.
* Klinefelter syndrome: Men with this condition, which is present at birth, have more than one X (female) chromosome. They have lower levels of androgens and higher levels of estrogen, which causes the testicles to be smaller than usual and to not produce functioning sperm cells, making them infertile. Klinefelter syndrome affects about one in 1,000 men.
* Testicle conditions: Having an undescended testicle, having mumps as an adult, or having one or both testicles surgically removed may increase risk of breast cancer in men.
* A family history of breast cancer: About 20 percent of men with breast cancer have close male or female relatives with the disease. However, most cases of male breast cancer occur in men without a family history of breast cancer or an inherited gene abnormality.
* Inherited gene mutations: Men who inherit abnormal BRCA1, BRCA2, CHEK2 or PTEN genes have an increased risk for breast cancer. A mutation in the gene BRCA2 accounts for about 10 percent of male breast cancer, whereas the risk is about 1 percent with the BRCA1 gene mutation. Overall, this is about 80 times greater than the lifetime risk of men without BRCA1 or BRCA2 abnormalities.
* Occupation: Men who work in hot environments, such as steel mills, may be at an increased risk. Long-term exposure to higher temperatures can affect the testicles, which in turn can affect hormone levels. Men chronically exposed to gasoline fumes may also have a higher risk.
* Radiation exposure: Having radiation therapy to the chest before the age of 30, as in patients who are treated for Hodgkin's disease, may increase the risk.
* Age: The risk of breast cancer in men increases as age increases. Although the disease can develop at any age, it is usually detected in men between 60 and 70 years of age. The median age of diagnosis for men is about 67.
(Source: National Cancer Institute, "Male Breast Cancer Treatment," February 5, 2008.)
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