What causes breast cancer?

The exact causes of breast cancer are not known. However, research has found that the following risk factors increase a woman's chance of developing the disease:

• Age. This is the most important factor. Most breast cancers occur in women over the age of 50, and the risk is especially high for women over age 60.
• A personal history of breast cancer.
• A family history of breast cancer (having a mother, sister, or daughter who has had the disease).
• A diagnosis of certain breast changes, such as atypical hyperplasia (a noncancerous condition in which cells look abnormal and are increased in number) and lobular carcinoma in situ (abnormal cells in the lobules of the breast.).
• Changes in certain genes (BRCA1, BRCA2, and others). These changes are rare. In families with many cases of breast cancer, they may sometimes be found through genetic testing.

Other factors linked to increased risk of breast cancer include:

• Long-term exposure to estrogen. This applies to women who began menstruation before age 12, experienced menopause after age 55, never had children, or took hormone replacement therapy for long periods of time. Women who took DES (diethylstilbestrol) during pregnancy also are at a slightly higher risk of breast cancer.
• Late childbearing (having a first child after age 30).
• Dense (not fatty) breast tissue. Breast cancers in older women nearly always develop in dense tissue.
• Radiation therapy. This may be a factor for women whose breasts were exposed to radiation therapy before age 30, especially those who were treated for Hodgkin's disease.
• Alcohol. Some studies have linked use of alcohol to a slightly higher breast cancer risk.

For more information about breast cancer risk or genetic counseling, call the Cancer Information Service at 1-800-4-CANCER.

Source:  "Ask the CIS" by the Cancer Information Service.  "Ask the CIS" is distributed by the Cancer Information Service (CIS) of the Heartland, which serves Kansas, Nebraska, Missouri & Illinois. The CIS is a program of the National Cancer Institute. Call the CIS toll-free at 1-800-4-CANCER (1-800-422-6237) between 9 a.m. and 4:30 p.m. local time.