Skip to main content

What Causes Breast Cancer in Men?

Although certain risk factors may increase a man's chances of developing breast cancer, the cause of most breast cancers in men is unknown.

Hormone levels

Breast cells normally grow and divide in response to female hormones such as estrogen. The more cells divide, the more chances there are for mistakes to be made when they are copying their DNA. These DNA changes can eventually lead to cancer (see below).

Factors that unbalance the levels of female and male hormones in the body can therefore have an effect on breast cancer risk. Many of these were described in Risk Factors for Breast Cancer in Men.

Gene changes (mutations)

Researchers are making great progress in understanding how certain changes in DNA can cause normal cells to become cancerous. DNA is the chemical in our cells that makes up our genes, the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. However, DNA affects more than how we look.

Some genes contain instructions for controlling when our cells grow, divide, and die. Certain genes that speed up cell division are called oncogenes. Others that slow down cell division or cause cells to die at the appropriate time are called tumor suppressor genes. Cancers can be caused by DNA mutations (defects) that turn on oncogenes or turn off tumor suppressor genes.

Acquired gene mutations

Most DNA mutations related to male breast cancer occur during life rather than having been inherited from a parent before birth. It's not clear what causes most of these mutations. Radiation to the breast area is a factor in a small number of cases. Some acquired mutations of oncogenes and/or tumor suppressor genes may be the result of cancer-causing chemicals in our environment or diet, but so far studies have not identified any chemicals that are responsible for these mutations in male breast cancers.

Inherited gene mutations

Certain inherited DNA changes can cause a high risk of developing certain cancers and are responsible for cancers that run in some families.

Some breast cancers are linked to inherited mutations of the BRCA1 or BRCA2 tumor suppressor genes. Normally, these genes make proteins that help cells recognize and/or repair DNA damage and prevent them from growing abnormally. But if a person has inherited a mutated gene from either parent, the chances of developing breast cancer are higher.

Men with inherited mutations in the BRCA1 and BRCA2 genes have a higher lifetime risk for breast cancer, and possibly some other cancers such as prostate and pancreatic cancer. There are also other hereditary cancer syndromes that can be associated with male breast cancer.

All men who have been diagnosed with breast cancer should consider genetic testing because they can be at risk for other cancers, such as prostate and pancreas cancer. Having one of these inherited gene changes might also affect their family members' chances of getting certain cancers.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

Burstein HJ, Harris JR, Morrow M. Ch. 79 - Malignant tumors of the breast. In: DeVita VT, Lawrence TS, Rosenberg SA, eds. DeVita, Hellman, and Rosenberg's Cancer: Principles and Practice of Oncology. 10th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2015.

Fentiman IS. Review: The biology of male breast cancer. The Breast 38 (2018) 132-135.

Fentiman IS, Fourquet A, Hortobagyi GN. Male breast cancer. Lancet. 2006; 367:595–604.

Giordano SH, Buzdar AU, Hortobagyi GN. Breast cancer in men. Ann Intern Med. 2002;137: 678–687.

Giordano SH, Cohen DS, Buzdar AU, et al. Breast cancer in men: a population-based study. Cancer. 2004;101: 51–57.

Jain S and Gradishar WJ. Chapter 61: Male Breast Cancer. In: Harris JR, Lippman ME, Morrow M, Osborne CK, eds. Diseases of the Breast. 5th ed. Philadelphia, Pa: Lippincott-Williams & Wilkins; 2014.

Liede A, Karlan BY, Narod SA. Cancer risks for male carriers of germline mutations in BRCA1 or BRCA2: a review of the literature. J Clin Oncol. 2004;22: 735–742.

Tai YC, Domchek S, Parmigiani G, Chen S. Breast cancer risk among male BRCA1 and BRCA2 mutation carriers. J Natl Cancer Inst. 2007;99: 1811−1814.

Wolff AC, Domchek SM, Davidson NE et al. Ch 91 - Cancer of the Breast. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 5th ed. Philadelphia, Pa: Elsevier: 2014.

Last Revised: April 27, 2018

American Cancer Society Emails

Sign up to stay up-to-date with news, valuable information, and ways to get involved with the American Cancer Society.