Breast Cancer Causes & Risk Factors

It is not always clear what causes breast cancer. However, there are certain known causes and risk factors. Sometimes, it is possible to take steps to reduce your risk factors, lowering your risk for getting breast cancer.

Gender is the most common risk factor for getting breast cancer. While men can also get the disease, it is about 100 times more common in women than in men. Other causes and risk factors include:

  • Age. Risk increases with age. About two-thirds of women with invasive breast cancer are 55 years or older when the cancer is detected.
  • Genetic risk factors. About five to 10 percent of breast cancers may be linked to certain inherited genetic mutations. If you have these genetic markers, you may have up to an 80 percent chance of getting breast cancer.
  • Family history. If you have close blood relatives with breast cancer, you have a higher risk as well. The relatives can be from either side of the family. If your mother, sister or daughter has breast cancer, then your risk is roughly doubled. However, it is important to note that 70 to 80 percent of breast cancer patients do not have any family history of the disease.
  • Personal history. If you already had breast cancer, then your chance of getting a new incidence of breast cancer is higher. (This is different from a recurrence of the first cancer.)
  • Race. Caucasian women are slightly more likely to get breast cancer than African-American women, but African-American women are more likely to die from the disease. Part of the reason may be that African-American women have faster growing tumors, though we don't know why. Asian, Hispanic and Native American women have a lower risk of getting and dying from breast cancer.
  • Dense breast tissue. Dense breast tissue increases your risk of breast cancer. This is because there is more gland tissue and less fatty tissue, making it more difficult for doctors to spot problems on mammograms.
  • Benign breast issues. Having certain benign breast changes may increase your risk of breast cancer.
  • Menstrual periods. A woman who has had more menstrual periods, and as a result had a greater exposure to the hormones estrogen and progesterone, has a slightly increased risk of breast cancer. This includes women who began menstruating before 12 years of age or who stopped menstruating after 55 years of age.
  • Earlier breast radiation. If you had radiation treatment for other cancers in the chest area, you have a higher risk of breast cancer. The risk is highest if you received the radiation as a teen, while the breasts were still developing.
  • Treatment with DES. In the past, some pregnant women took the drug DES (diethylstilbestrol) because it was thought to reduce the possibility of miscarriage. Recent studies have shown that these women (and daughters who were exposed to DES while in the womb) have a slightly increased risk of getting breast cancer.
  • Not having children/having children later in life. Women who haven't had children, or those who had their first child after age 30, have a slightly higher risk of breast cancer. Having multiple pregnancies and having them at an early age reduces breast cancer risk. This may be because pregnancy lowers the total number of lifetime menstrual cycles.
  • Using birth control pills. Women who use birth control pills have a slightly higher risk of breast cancer than women who never used them. However, once you stop using the pills, the risk dissipates, and after 10 years, the risk more or less disappears.
  • Using post-menopausal hormone therapy. Some women use hormone therapy to relieve symptoms of menopause and help prevent osteoporosis. If you still have a uterus, your doctor will probably prescribe estrogen and progesterone, since estrogen alone can increase cancer risk.
  • Not breastfeeding. Breastfeeding can slightly lower breast cancer risk, especially if it lasts more than a year. This may be because breastfeeding lowers your total number of menstrual periods.
  • Alcohol. If you drink two or more drinks per day, your risk is about one-and-a-half times the risk of a woman who drinks no alcohol.
  • Overweight. Obesity is linked to an increased breast cancer risk, especially if you gained weight later in life.
  • Lack of exercise. Exercise may reduce breast cancer risk. Even as little as one to two hours of walking per week reduced risk by 18 percent.
  • Night work. Recent studies showed that women who work night shifts have a higher risk of breast cancer.