The genes most commonly affected in hereditary breast and ovarian cancer are the breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) genes. About 3% of breast cancers (about 6,000 women per year) and 10% of ovarian cancers (about 2,000 women per year) result from inherited mutations in the BRCA1 and BRCA2 genes.
Normally, the BRCA1 and BRCA2 genes protect you from getting certain cancers. But some mutations in the BRCA1 and BRCA2 genes prevent them from working properly, so that if you inherit one of these mutations, you are more likely to get breast, ovarian, and other cancers. However, not everyone who inherits a BRCA1 or BRCA2 mutation will get breast or ovarian cancer.
Everyone has two copies of the BRCA1 and BRCA2 genes, one copy inherited from their mother and one from their father. Even if a person inherits a BRCA1 or BRCA2 mutation from one parent, they still have the normal copy of the BRCA1 or BRCA2 gene from the other parent. Cancer occurs when a second mutation happens that affects the normal copy of the gene, so that the person no longer has a BRCA1 or BRCA2 gene that works properly. Unlike the inherited BRCA1 or BRCA2 mutation, the second mutation would not be present throughout the person’s body, but would only be present in the cancer tissue.
Breast and ovarian cancer can also be caused by inherited mutations in genes other than BRCA1 and BRCA2. This means that in some families with a history of breast and ovarian cancer, family members will not have mutations in BRCA1 or BRCA2, but can have mutations in one of these other genes. These mutations might be identified through genetic testing using multigene panels, which look for mutations in several different genes at the same time.
You and your family members are more likely to have a BRCA1 or BRCA2 mutation if your family has a strong history of breast or ovarian cancer. Family members who inherit BRCA1 and BRCA2 mutations usually share the same mutation. If one of your family members has a known BRCA1 or BRCA2 mutation, other family members who get genetic testing should be checked for that mutation.
If you are concerned that you could have a BRCA1, BRCA2, or other mutation related to breast and ovarian cancer, the first step is to collect your family health history of breast and ovarian cancer and share this information with your doctor.