Risk Factors for Breast Cancer

Although there is no perfect way to predict whether a woman will have breast cancer, there are certain known factors that increase the risk of breast cancer. How much each risk factor increases or decreases an individual woman's risk is difficult to calculate, however. Additionally, many risk factors, such as family history, are outside of an individual woman's control. Lifestyle factors such as diet, alcohol consumption, exercise and body weight are areas in which a woman can affect her breast cancer risk to some degree.

Known risk factors include:

  • Age. Breast cancer risk increases with age. Two of three women with invasive breast cancer are older than 55.
  • Age of menstruation. Women who began menstruating before age 12 or who continue menstruating past age 55 have a higher risk of breast cancer, probably due to the lifetime exposure to related hormones.
  • Alcohol consumption. Women who consume two to five alcoholic drinks a day are 1.5 times more likely to have breast cancer than are women who drink less.
  • Chemical or radiation exposure. Women who had chest radiation treatments before they turned 30 or who whose mothers took the synthetic estrogen diethylstilbestrol (DES) while they were pregnant have an increased risk of breast cancer.
  • Diet. Women who get take in less than the recommended amount of vitamin D have a higher risk of breast cancer. Studies have shown that a diet rich in leafy greens, fruits, vegetables, lean meats and whole grains is the best choice for overall cancer prevention.
  • Family history. Genes play an important role in breast cancer risk. About 10 percent of breast cancers may be genetic in origin. Mutations in two specific genes, BRCA1 and BRCA2, have been found to be strongly related to breast cancer risk. Women whose blood relatives have had breast cancer are at increased risk. Up to 30 percent of women with breast cancer have a relative who has been diagnosed with the disease. Breast cancer in a father, mother, daughter, sister or brother strongly increase a woman's risk. For instance, recent research showed that women whose sisters had been diagnosed with breast cancer were six times more likely to develop breast cancer themselves than were women whose sisters did not have breast cancer.
  • Obesity and overweight. Although the exact nature of the relationship between excess body fat and breast cancer is not fully understood, women who are overweight or obese (particularly those who are post-menopausal) have an increased risk of a breast cancer diagnosis.
  • Physical activity. The more physically active a woman is, the less likely she is to be diagnosed with breast cancer. According to an analysis of data from the Nurses Health Study II, women who walked 13 hours a week or ran 3.25 hours weekly had a 23 percent lower risk of breast cancer than their less-active peers.
  • Pregnancies. Having a first child after age 30 or not bearing children at all increases breast cancer risk. In contrast, being pregnant more than once or having children before age 30 seems to reduce breast cancer risk.
  • Prior breast cancer diagnosis. Once a woman has had breast cancer, her risk of a recurrence is nearly four times the risk of a breast cancer diagnosis faced by a woman who's never had the disease.
  • Race. White women have the highest risk of a breast cancer diagnosis, but African American women are more likely to die from breast cancer. Although the reason for this disparity is not fully understood, experts suggest that African American women may have more aggressive cancers, making the cancer more difficult to treat. Hispanic, Asian and Native American women all have much lower breast cancer risk profiles.
  • Related health measures. Higher-than-average bone mineral density levels are predictive of a greater risk of breast cancer. Similarly, certain benign breast growths as well as changes in the tissues of the milk ducts also increase breast cancer risk.

SOURCES: "Familial Breast Cancer Risk Lasts a Lifetime for Sisters," May 13, 2008, HealthDay News; "Low Levels of Vitamin D Spell Trouble for Breast Cancer Patients," May 16, 2008, HealthDay News; "Bone Density Predicts Risk of Breast Cancer," July 28, 2008, HealthDay News; American Cancer Society (www.cancer.org); National Cancer Institute (www.cancer.gov)

Written by Madeline Roberts Vann, MPH

Reviewed by Susan L. Luedke, MD

St. Louis Cancer & Breast Institute

St. Louis University Medical Center

Last updated September 2008