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
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.