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:
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Diagnosis of bilateral breast cancer (cancer in both breasts)
Being of Ashkenazi Jewish descent
Having ovarian cancer with or without a family history of breast or ovarian cancer
Having a male in the family with breast cancer
Diagnosis of triple negative breast cancer under age 60
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 1,000 mutations of these genes exist. Specific mutations in these genes are associated with an increased breast cancer risk.
An estimated 1 in 800 women carry the BRCA1 gene and 1 in 1,000 women are carriers of the BRCA2 gene. 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.