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What Are the Risk Factors for Breast Cancer?

Studies have shown that your risk for breast cancer is due to a combination of factors. The main factors that influence your risk include being a woman and getting older. Most breast cancers are found in women who are 50 years old or older.

Some women will get breast cancer even without any other risk factors that they know of. Having a risk factor does not mean you will get the disease, and not all risk factors have the same effect. Most women have some risk factors, but most women do not get breast cancer. If you have breast cancer risk factors, talk with your doctor about ways you can lower your risk and about screening for breast cancer.

Risk factors include—

  • Getting older. The risk for breast cancer increases with age; most breast cancers are diagnosed after age 50.
  • Genetic mutations. Inherited changes (mutations) to certain genes, such as BRCA1 and BRCA2. Women who have inherited these genetic changes are at higher risk of breast and ovarian cancer.
  • Early menstrual period. Women who start their periods before age 12 are exposed to hormones longer, raising the risk for breast cancer by a small amount.
  • Late or no pregnancy. Having the first pregnancy after age 30 and never having a full-term pregnancy can raise breast cancer risk.
  • Starting menopause after age 55. Like starting one’s period early, being exposed to estrogen hormones for a longer time later in life also raises the risk of breast cancer.
  • Not being physically active. Women who are not physically active have a higher risk of getting breast cancer.
  • Being overweight or obese after menopause. Older women who are overweight or obese have a higher risk of getting breast cancer than those at a normal weight.
  • Having dense breasts. Dense breasts have more connective tissue than fatty tissue, which can sometimes make it hard to see tumors on a mammogram. Women with dense breasts are more likely to get breast cancer.
  • Using combination hormone therapy. Taking hormones to replace missing estrogen and progesterone in menopause for more than five years raises the risk for breast cancer. The hormones that have been shown to increase risk are estrogen and progestin when taken together.
  • Taking oral contraceptives (birth control pills). Certain forms of oral contraceptive pills have been found to raise breast cancer risk.
  • Personal history of breast cancer. Women who have had breast cancer are more likely to get breast cancer a second time.
  • Personal history of certain non-cancerous breast diseases. Some non-cancerous breast diseases such as atypical hyperplasia or lobular carcinoma in situ are associated with a higher risk of getting breast cancer.
  • Family history of breast cancer. A woman’s risk for breast cancer is higher if she has a mother, sister, or daughter (first-degree relative) or multiple family members on either her mother’s or father’s side of the family who have had breast cancer. Having a first-degree male relative with breast cancer also raises a woman’s risk.
  • Previous treatment using radiation therapy. Women who had radiation therapy to the chest or breasts (like for treatment of Hodgkin’s lymphoma) before age 30 have a higher risk of getting breast cancer later in life.
  • Women who took the drug diethylstilbestrol (DES), which was given to some pregnant women in the United States between 1940 and 1971 to prevent miscarriage, have a higher risk. Women whose mothers took DES while pregnant with them are also at risk.
  • Drinking alcohol. Studies show that a woman’s risk for breast cancer increases with the more alcohol she drinks.

Research suggests that other factors such as smoking, being exposed to chemicals that can cause cancer, and night shift working also may increase breast cancer risk.