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Causes

By Mayo Clinic staff

Living With Cancer

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It's not clear what causes breast cancer. Doctors know that breast cancer occurs when some breast cells begin growing abnormally. These cells divide more rapidly than healthy cells do and continue to accumulate, forming a lump or mass. The cells may spread (metastasize) through your breast to your lymph nodes or to other parts of your body.

Breast cancer most often begins with cells in the milk-producing ducts (invasive ductal carcinoma). Breast cancer may also begin in the glandular tissue called lobules (invasive lobular carcinoma) or in other cells within the breast.

Researchers have identified things that can increase your risk of breast cancer. But it's not clear why some people who have no risk factors develop cancer, yet other people with risk factors never do. It's likely that breast cancer is caused by a complex interaction of your genetic makeup and your environment.

Inherited breast cancer
Doctors estimate that only 5 to 10 percent of breast cancers are linked to gene mutations passed through generations of a family. A number of inherited mutated genes that can increase the likelihood of breast cancer have been identified. The most common are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2), both of which increase the risk of both breast and ovarian cancer.

If you have a strong family history of breast cancer or other cancers, blood tests may help identify mutations in BRCA or other genes that are being passed through your family.

Consider asking your doctor for a referral to a genetic counselor, who can review your family health history. A genetic counselor can also discuss the benefits, risks and limitations of genetic testing with you.

Risk factors Symptoms
References
  1. Breast cancer. Fort Washington, Pa.: National Comprehensive Cancer Network. http://www.nccn.org/professionals/physician_gls/f_guidelines.asp. Accessed March 13, 2013.
  2. Townsend CM Jr., et al. Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice. 19th ed. Philadelphia, Pa.: Saunders Elsevier; 2012. http://www.mdconsult.com/das/book/body/208746819-6/0/1565/0.html. Accessed March 13, 2013.
  3. Breast cancer treatment (PDQ). National Cancer Institute. http://cancer.gov/cancertopics/pdq/treatment/breast/Patient. Accessed March 18, 2013.
  4. Leading new cancer cases and deaths — 2013 estimates. American Cancer Society. http://www.cancer.org/research/cancerfactsfigures/cancerfactsfigures/cancer-facts-figures-2013-most-requested-tables-figures. Accessed March 18, 2013.
  5. SEER stat fact sheet: Breast. National Cancer Institute. http://seer.cancer.gov/statfacts/html/breast.html. Accessed March 18, 2013.
  6. Breast cancer prevention (PDQ). National Cancer Institute. http://cancer.gov/cancertopics/pdq/prevention/breast/Patient. Accessed March 13, 2013.
  7. What you need to know about breast cancer. National Cancer Institute. http://cancer.gov/cancertopics/wyntk/breast. Accessed March 13, 2013.
  8. Hormone therapy for breast cancer. National Cancer Institute. http://cancer.gov/cancertopics/factsheet/Therapy/hormone-therapy-breast. Accessed March 18, 2013.
  9. Cancer-related fatigue. Fort Washington, Pa.: National Comprehensive Cancer Network. http://www.nccn.org/professionals/physician_gls/f_guidelines.asp. Accessed March 18, 2013.
  10. AskMayoExpert. Mammogram screening guidelines. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2012.
  11. Faslodex (prescribing information). Wilmington, Del.: AstraZeneca; 2012. http://www.faslodex.com. Accessed March 18, 2013.
  12. Herceptin (prescribing information). South San Francisco, Calif.: Genentech, Inc.; 2010. http://www.herceptin.com. Accessed March 18, 2013.
  13. Perjeta (prescribing information). South San Francisco, Calif.: Genentech, Inc.; 2012. http://www.perjeta.com. Accessed March 18, 2013.
  14. Kadcyla (prescribing information). South San Francisco, Calif.: Genentech, Inc.; 2013. http://www.kadcyla.com. Accessed March 18, 2013.
  15. Tykerb (prescribing information). Research Triangle Park, N.C.: GlaxoSmithKline; 2012. http://www.tykerb.com. Accessed March 18, 2013.
  16. Breast SPOREs. National Cancer Institute. http://trp.cancer.gov/spores/breast.htm. Accessed March 19, 2013.
  17. Moynihan TJ (expert opinion). Mayo Clinic, Rochester, Minn. March 19, 2013.
  18. Pruthi S (expert opinion). Mayo Clinic, Rochester, Minn. March 21, 2013.
DS00328 May 22, 2013

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