Risk Factors

There are no known definitive causes of most breast cancers. However, epidemiologic studies have identified some factors that appear to be associated with a woman's risk for developing breast cancer. Simply being a woman and getting older increases a woman's risk for developing breast cancer, yet having one or more of these factors does not necessarily mean one will develop breast cancer.

While the risk factors described below have been determined by epidemiological studies to increase a woman's chance of developing breast cancer, it is important to note that having any of these risk factors does not necessarily mean that one will develop breast cancer. In fact, 70% of all breast cancer cases are found in women who do not have any known risk factors. If you are concerned about your risk of developing breast cancer, speak with your personal health care provider about steps you can take to reduce your risk.


Evidence suggests that the longer a woman is exposed to the hormone estrogen (made by the body, taken as a drug, or delivered by a patch), the more likely she is to develop breast cancer. Below are hormonal factors related to breast cancer risk:

  • Early menarche (before age 13)
  • Late menopause (after age 55)
  • Never having given birth
  • Having a first born child at an older age (after age 30)
  • Having never breast fed a child
  • Taking hormone replacement therapy (5 or more years, possibly only if combined estrogen and progesterone)
  • Recent oral contraceptive use
  • Having taken DES (diethylstilbestrol, a synthetic estrogen used between the 1940s and 1971) during pregnancy
  • Obesity after menopause (Fat tissue, especially around the waist, can change some hormones into estrogen.)
  • Personal history of breast cancer (Previous breast cancer increases the risk of developing cancer in the other breast.)


The following breast conditions are associated with an increased risk for developing breast cancer:

  • Atypical hyperplasia lobular carcinoma in situ
  • Higher breast density (The majority of breast cancer develops in the lobular or ductal tissues, and a high proportion of lobular and ductal tissue appears dense on mammograms making it more difficult to see abnormalities.)
  • Radiation therapy (Exposure to high-dose ionizing radiation before age 30 is associated with an increased risk for developing breast cancer.)


Known genetic factors explain only a small proportion (5%-10%) of breast cancer incidence. Yet those women with specific genetic traits have a 50% to 80% chance of developing breast cancer in their lifetime. Inherited genetic factors include:

  • Family history
    A woman's risk for developing breast cancer increases if her mother, sister, or daughter had breast cancer, especially at a young age, and is higher if more than one first-degree relative developed cancer.
  • Breast cancer gene mutations
    Women with mutations in breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) genes tend to have cancers that occur at a younger age.
  • Damaged tumor suppressor genes
    Women with a damaged tumor prevention gene called p53 tend to develop a breast cancer that is more aggressive.


  • High socioeconomic status
  • Urban residence
  • Tall height
  • Genetics
  • Excessive alcohol consumption (more than 2 drinks/day)


These are things you can do to decrease your risk of developing breast cancer:

  • Be physically active everyday
  • Keep off excess weight
  • If you are going to give birth, breastfeed your baby
  • Eat 5 or more servings of fruits and vegetables everyday
  • Quit smoking
  • Follow the precautionary principle and limit exposure to potentially harmful chemicals