It's not clear what causes male breast cancer. Doctors know that male breast cancer occurs when some breast cells begin growing abnormally. These cells divide more rapidly than healthy cells do. The accumulating cells form a tumor that may spread (metastasize) to nearby tissue, to the lymph nodes or to other parts of the body.

Where breast cancer begins in men

Everyone is born with a small amount of breast tissue. Breast tissue is made up of milk-producing glands (lobules), ducts that carry milk to the nipples and fat. Women begin developing more breast tissue during puberty and men do not. Because men are born with a small amount of breast tissue, they can develop breast cancer.

Types of breast cancer diagnosed in men include:

  • Cancer that begins in the milk ducts. Ductal carcinoma is the most common type of male breast cancer. Nearly all male breast cancers begin in the milk ducts.
  • Cancer that begins in the milk-producing glands. Lobular carcinoma is rare in men because men have few lobules in their breast tissue.
  • Cancer that spreads to the nipple. In some cases, breast cancer can form in the milk ducts and spread to the nipple, causing crusty, scaly skin around the nipple. This is called Paget's disease of the nipple.

Inherited genes that increase breast cancer risk

Some men inherit mutated genes from their parents that increase the risk of breast cancer. Mutations in one of several genes, especially a gene called BRCA2, put you at greater risk of developing breast and prostate cancers. The normal function of these genes is to help prevent cancer by making proteins that keep cells from growing abnormally. But if they have a mutation, the genes aren't as effective at protecting you from cancer.

Meeting with a genetic counselor and undergoing genetic testing can determine whether you carry gene mutations that increase your risk of breast cancer. Discuss the benefits and risks of genetic testing with your doctor.

Feb. 25, 2012