Causes and Risk Factors

The average risk of developing breast cancer over your lifetime is 10 to 12 percent, or one in nine. But some women have a higher risk than others. Most women who develop breast cancer do not have any known risk factors.

A risk factor is something that increases your chances of developing the disease. For instance, breast cancer is more common in Caucasian women ages 50 and older. This does not mean that a 60-year-old Caucasian woman is sure to develop cancer. It just means she has a higher risk than a younger woman or a woman of color.

Genetic and environmental factors combine to cause breast cancer. The risk factors that we know about include:

  • Being overweight, particularly after menopause
  • Diagnosed changes in breast tissue such as atypical ductal hyperplasia, atypical lobular hyperplasia, or LCIS
  • Excessive alcohol drinking
  • Family members with breast cancer
  • Genetic mutations, including the BRCA1 and BRCA2 genes
  • Having very dense breasts, as seen on a  mammogram
  • Increased estrogen over a lifetime as a result of 
    • getting your period early
    • experiencing late menopause
    • having children after age 35 or not at all
    • not breastfeeding
    • undergoing hormone replacement therapy
  • Personal history of breast cancer
  • Radiation therapy before age 30

The Center of Excellence for Breast Cancer at the Mount Sinai Health System runs a surveillance program for women at high risk of developing breast cancer. If you think you may be at high risk, you can participate in our Cancer Risk Evaluation (CaRE) program. The program not only helps you understand your risk, but can assist in reducing or managing that risk. If you have a high risk of breast cancer, we can give you an individualized plan, teach you about your risk, and monitor you carefully. To determine high risk, we use the most up-to-date imaging techniques as well as genetic counseling. We also offer therapies to reduce the risk of breast cancer in select high-risk women.

The factors that put women at highest risk for breast cancer include:  

  • A first-degree relative (a parent or sibling) with breast or ovarian cancer
  • Multiple family members with breast cancer
  • Family history of:
    • Male breast cancer
    • Premenopausal breast cancer
    • Ovarian cancer
  • A personal diagnosis or history of:
    • BRCA or other high risk mutation
    • Hodgkin’s lymphoma
    • Lobular carcinoma in situ (LCIS), atypia, or other related conditions