Breast Cancer and Your Genes

Women with a family history of breast cancer make up about 5% to 10% 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:

About Genes

Each of us is born with two copies of about 100,000 different genes in each cell. 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 the mutated BRCA1 gene have a 65% risk of breast cancer recurrence. Bilateral breast cancer (cancer in both breasts) is also common in women who carry the mutated BRCA1.

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. 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 Reviewed by Jennifer Robinson, MD on August 31, 2015



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


National Comprehensive Cancer Network.

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

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