The Role of Genetics in Breast Cancer

Institutes & Services > Women's Services

Among all women with breast cancer, about 5 to 10% have a genetic risk for the disease. Having a direct relative with breast cancer (mother, sister, daughter) on either the mother’s or father’s side presents the greatest risk to other women in the family. Women with this direct family connection have a risk 3 to 5 times larger than women with no direct relatives with breast cancer.

Characteristics that can suggest a breast cancer gene:

  • Developing breast cancer before age 50
  • Having several family members with breast and/or ovarian cancer
  • Developing breast cancer in both breasts

Breast Cancer Genes

Genes are very small pieces of DNA that govern how cells work, including how and when they divide and grow. We inherit one copy of each gene from our mothers and one from our fathers.

Mutations are changes or abnormalities that make the cells work differently. Women with breast cancer may have more than one of these mutations.

BRCA1 was the first gene identified as increasing a woman’s risk for ovarian and breast cancer. It’s estimated that 1 in 600 women have this gene. Having the BRCA1 gene means a woman has an 80% risk of developing breast or ovarian cancer by the time she is 85. In addition, this gene means she has a 60% risk of getting a second breast cancer.

BRCA2 is another gene mutation linked with breast cancer. As yet, scientists don’t know as much about this gene, although studies suggest that it may be associated with breast cancer in males.

Since both BRCA1 and BRCA2 can be inherited from either parent, it’s important to know the father’s family history with breast cancer. Mothers and fathers with either gene mutation have a 50/50 chance of passing it to each of their children. 

Not all women who carry the BRCA1 and BRCA2 genes will get cancer. Those who do have either gene mutation may be more likely to develop breast or ovarian cancer and they usually have a greater risk of getting breast cancer at a younger age – before they are 50.

Genetic Testing for Breast Cancer

Genetic testing can determine whether the BRCA1 or BRCA2 genes are present. It can also determine whether a woman who has already been diagnosed with breast cancer has a higher risk of getting a second breast cancer or ovarian cancer. However, genetic testing is usually only done when a strong family or personal history is present.

If you are interested in the possibility of genetic testing, you should first meet with a board-certified and licensed genetic counselor to determine your risk and to understand options.

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