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.
- Other types of cancer. Other, rarer types of breast cancer that can occur in men include Paget's disease of the nipple and inflammatory breast cancer.
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.
If you have a strong family history of cancer, discuss this with your doctor. Your doctor may recommend that you meet with a genetic counselor in order to consider genetic testing to see if you carry genes that increase your risk of cancer.