Non-Genetic Risk Factors

Most cases of cancer are not hereditary or familial in nature.  As you can see in the pie chart below, only about 5-10% of breast cancer is hereditary in nature, about 20-25% is familial - meaning there are multiple family members affected with breast cancer, but the pattern of affected family members does not follow the pattern expected with a hereditary predisposition syndrome (see Genetic Risk Factors for more information), and about 70-75% is sporadic in nature - meaning there is not a significant family history of breast or ovarian cancer.


Genes are one of many risk factors that could be associated with an individual’s breast cancer risk.

Other factors include:

  • Personal history of breast cancer
  • Family history
  • Age
  • Ethnicity
  • Age of menarche
  • Age of menopause
  • Age of first term pregnancy
  • Hormone replacement therapy
  • Abnormal breast biopsy
  • Previous chest irradiation
  • Obesity/level of physical activity
  • Alcohol