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Breast Cancer and Your Genes

Medically Reviewed by Laura J. Martin, MD on November 05, 2019

Women with a family history of breast cancer make up about 15% of all women with the disease. Having a close relative (mother, sister, or daughter) with breast cancer doubles your risk compared to that of other women.

If any of the following are true for you, there’s an increased likelihood you carry a breast cancer gene:

  • You were diagnosed with breast cancer before age 45.
  • You have several family members diagnosed with breast or ovarian cancer.
  • You have ovarian cancer.
  • You are of Ashkenazi Jewish descent.
  • A male in your family has or had breast cancer.
  • You were diagnosed with bilateral breast cancer (cancer in both breasts).
  • You were diagnosed with triple negative breast cancer before the age of 60.

 

About Genes

Each cell in the body has about 20,500 genes. Genes are tiny segments of DNA that control how cells function. One copy of each gene comes from your mother. The other is from your father.

Genes can develop abnormalities that change how the cell works.

Breast Cancer Genes

Abnormalities (mutations) in two genes -- BRCA1 and BRCA2 - are the most common causes of hereditary breast cancer, accounting for about 20% to 25% of cases.

Usually, BRCA genes help to prevent cancer by creating proteins that keep cells from growing abnormally. If you inherit a mutated BRCA1 or BRCA2, you’re more likely to develop cancer during your lifetime.

 

Family Ties

If either of your parents carries one of these mutations, you have a 50% chance of having it, as well. And if you have it, you can pass it on to your children. However, it's important to note that not everyone who carries these mutated genes will develop cancer.

Know the Risks

Women who inherit the mutated BRCA1 gene have a 55% to 65% risk of developing breast cancer by age 70. Women with the mutated BRCA2 have around a 45% risk.

Either mutation brings an increased risk of developing breast cancer at a younger age (before menopause).

People who have a mutated BRCA1 or BRCA2 gene have an increased risk of developing a second primary breast cancer. Bilateral breast cancer (cancer in both breasts) is also more common in women who carry a BRCA 1 or BRCA2 gene.

Both mutations also increase your risk of other cancers, especially ovarian cancer.

Who Gets Tested

At-risk families can take blood tests to screen for mutations in these genes. But genetic testing is done only when there’s a strong personal or family history or other risk factors. The screening can also help determine if a woman who has already been diagnosed with breast cancer is at an increased risk for a second breast cancer or ovarian cancer.

WebMD Medical Reference

Sources

SOURCES: 

The American Cancer Society: "Breast cancer risk factors you cannot change" and "Genetic Testing: What You Need to Know."

CDC.

National Comprehensive Cancer Network.

National Cancer Institute: "BRCA1 and BRCA2: Cancer Risk and Genetic Testing."

NIH: "An Overview of the Human Genome Project."

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