It's not clear what causes male breast cancer.

Doctors know that male breast cancer occurs when some breast 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 consists of milk-producing glands (lobules), ducts that carry milk to the nipples, and fat.

During puberty, women begin developing more breast tissue, and men do not. But 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). Nearly all male breast cancer is ductal carcinoma.
  • Cancer that begins in the milk-producing glands (lobular carcinoma). This type is rare in men because they have few lobules in their breast tissue.
  • Cancer that spreads to the nipple (Paget's disease of the nipple). Rarely, male breast cancer forms in the milk ducts and spreads to the nipple, causing crusty, scaly skin around the nipple.

Inherited genes that increase breast cancer risk

Some men inherit abnormal (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.

These genes normally make proteins that keep cells from growing abnormally — which helps prevent cancer. But mutated 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 — and if you can pass this gene along to your children, both boys and girls. Discuss the benefits and risks of genetic testing with your doctor.

Feb. 17, 2015

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