Breast Cancer and Your Genes

Women with a family history of breast cancer account for 5% to 10% of all women with the 

disease. Having a close relative (mother, sister, or daughter) with breast cancer poses the 

greatest risk to other female members of the family, doubling the risk compared to that of the 

general population.

Several characteristics may suggest that a woman has a breast cancer gene:

• Diagnosis of breast cancer before age 40
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• Several family members diagnosed with breast and/or ovarian cancer
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• Diagnosis of bilateral breast cancer (cancer in both breasts)
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• Being of Ashkenazi Jewish descent
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• Having ovarian cancer with or without a family history of breast or ovarian cancer
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• Having a male in the family with breast cancer

What Are Breast Cancer Genes?

Each of us is born with two copies of about 100,000 different genes contained 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.

A gene can develop an abnormality that changes how the cell works. Abnormalities in two 

genes -- BRCA1 and BRCA2 -- have been found in some women with breast cancer. Over 

200 mutations of these genes exist. Specific mutations in these genes are associated with an 

increased breast cancer risk.

An estimated one in 800 women carry the BRCA1 gene (the number of carriers of BRCA2 

remain unknown). Women with inherited changes in either of these genes have up to an 85% 

chance of developing breast cancer in their lifetime.

The risk of developing a second breast cancer among individuals carrying the BRCA1 gene 

is 65%. Bilateral breast cancer (cancer in both breasts) is also common in women who carry 

the mutated form of this gene.

Although less is known about the BRCA2 gene, scientists do know that mutations in the gene 

are associated with a similar risk of developing breast cancer among carriers. Alterations in 

the BRCA2 gene may also account for a small percentage (6%) of male breast cancer.

Both mutations in the BRCA1 and BRCA2 genes can be inherited from either parent. 

Therefore, the father's family history of breast cancer is also important. Men or women who 

carry one of these gene mutations have a 50/50 chance of passing it on to each of their 

children.

Usually, these BRCA genes help to prevent cancer by creating proteins that keep cells from 

growing abnormally. But, if a changed or mutated BRCA1 or BRCA2 is inherited, you may 

be more susceptible to developing cancer during your lifetime. In addition, women with an 

altered BRCA gene usually have an increased risk of developing breast cancer at a younger 

age (before menopause). However, it's important to note that not all women who carry these 

genes will develop cancer.

Mutations in genes other than BRCA1 and BRCA2 have been shown, or are suspected, to play a role in increasing a person's risk of breast cancer.

At-risk families can take blood tests to screen for mutations in these genes. However, genetic testing is done only when definitely indicated by a strong personal or family history. Genetic testing may also be used to 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.