Around 12% of women will develop breast cancer sometime during their lives. Mutations to the BRCA1 and BRCA2 genes account for 3–5% of all breast cancers and 20–25% of hereditary breast cancers.
The BRCA genes are human tumor-suppressing genes, meaning they produce a tumor-suppressor protein to help repair damaged DNA in a cell. When working properly, these proteins fix the DNA damage, thus preventing the formation and growth of tumors. When tumor suppressor genes are mutated or altered, as can occur in harmful BRCA1 and BRCA2 mutations, the proteins they should produce may not function properly or be created at all, so DNA damage cannot be repaired. This outcome could potentially result in DNA changes that lead to cancer. Inherited mutations (i.e., mutations that are handed down from parent to child) in BRCA1 and BRCA2 are associated with an increase in the risk of female breast cancer, among other cancers.
According to recent estimates by the National Cancer Institute, 55–65% of women with a harmful BRCA1 mutation and 45% of women with a harmful BRCA2 mutation will develop breast cancer by the age of 70. Harmful BRCA1 and BRCA2 mutations can be inherited from mother or father. Harmful mutations in BRCA1 and BRCA2 are associated with higher prevalence in people of Ashkenazi Jewish descent, but mutations in these genes are seen in all racial and ethnic groups.
The BRCA gene test analyzes DNA, gathered from a blood or saliva sample, to identify mutations in either BRCA1 or BRCA2. The test is usually offered to people who are likely to have the inherited mutation(s) based on familial history or who have a certain types of breast cancer. A positive BRCA1 or BRCA2 gene mutation test result indicates that person has inherited a harmful mutation and has an increased risk of developing breast cancer. Additionally, both men and women who inherit harmful BRCA1 or BRCA2 may pass the mutation to their children, regardless of the parent developing cancer.
Direct medical harms of BRCA genetic testing are minimal, but results have a potential to negatively affect a person’s social and family life, emotions, finances, and healthcare choices.