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What Are the Risk Factors for Breast Cancer?

While some of the factors that put patients at risk for breast cancer, such as genetics or simply being female, cannot be changed, others are variable in that they are related to environmental conditions or lifestyle choices. Breast cancer risk factors include (but are not limited to):

  • Gender: Breast cancer incidence is 100 times greater in women than in men.
  • Genetics: Researchers now estimate that about 5 to 10 percent of breast cancer cases are caused by inherited genetic mutations. Most frequently, mutations in genes called BRCA1 and BRCA2 are involved, but mutations in certain other genes are believed to increase risk as well.
  • Family History: Breast cancer occurs more frequently in patients for whom at least one blood relative has been diagnosed with the disease. If a woman has one first-degree relative (mother, sister, or daughter) who has had breast cancer, her lifetime breast cancer risk doubles. Women with two first-degree relatives who have had breast cancer are at three times greater risk than the average woman. However, the majority of women (85 percent) diagnosed do not have a family history of breast cancer.
  • Personal History: A woman with a previous breast cancer diagnosis is 3 - 4 times more likely to develop a new cancer in the other breast or a different location in the same breast.
  • Ethnic or Racial Background: White women of non-Hispanic origin are more likely to develop breast cancer than are African-American women. However, African-American women are more likely to die of breast cancer. Asian, Hispanic, and Native American women are more likely to develop breast cancer before age 45.
  • Age: Breast cancer risk increases with age. Two thirds of breast cancer diagnoses occur in women age 55 or older, while 12.5 percent of female breast cancer cases are under age 45.
  • Age at First Menstrual Period: Breast cancer risk is increased slightly in women who began menstruating before age 12.
  • Age of Menopause: Late onset of menopause (after age 55) also slightly increases breast cancer risk.
  • Dense Breast Tissue: Increased breast-tissue density results from a higher proportion of glandular tissue and less fatty tissue. Normally, a woman and her doctor will not know that she has dense breast tissue until it is noted on her first mammogram. Since dense breast tissue makes it more difficult to detect possible tumors on a mammogram, additional screening methods, such as breast MRI, may be recommended for women with dense breast tissue. For further details about the very important issue of breast tissue density, please visit our Am I Dense? page.
  • History of Benign (Noncancerous) Breast Conditions: Some (but not all) noncancerous breast conditions, such as ductal hyperplasia, fibroadenoma, and sclerosingadenosis, slightly increase a woman’s risk of developing breast cancer.
  • History of Radiation Therapy to the Chest: Patients who have undergone past radiation therapy for cancers in the chest area (other than breast cancer) have a slightly increased breast cancer risk.
  • Various Lifestyle Factors: Among the lifestyle-related factors that may affect breast cancer risk for women are:
    • Having no children, or having the first child after age 30
    • Recent oral contraceptive use (less than 10 years ago)
    • Combined hormone therapy (with both estrogen and progesterone) after menopause
    • Alcohol use
    • Being overweight or obese, especially after menopause
    • Lack of regular exercise or physical activity

The above should be viewed as a representative but not comprehensive discussion of breast cancer risk factors. Most importantly, you should also make sure your doctor is fully informed about your personal and family history of breast cancer and its risk factors. For example, if breast cancer has occurred in your immediate family, other risk factors, such as lifestyle issues, may be of more concern. If fully informed, your primary-care physician will be in a better position to help you develop a breast cancer prevention and screening plan that better fits your individual needs.