FACTS ABOUT THE GENETICS OF BREAST CANCER

Currently two genes have been found that are associated with site-specific breast cancer: BRCA1 and BRCA2. These are single, dominantly inherited predisposition genes that confer a high risk for developing breast and/or ovarian cancer.

The BRCA1 gene is located on the long arm of chromosome 17. It is present in about half of the families with early-onset breast cancer and 80% of families with breast and ovarian cancer. Women who inherit mutations in the BRCA1 gene have an 85% chance of developing breast cancer by age 60, and a 55% risk for ovarian cancer. Men who inherit the BRCA1 gene mutation are more likely to develop prostate cancer.

The BRCA2 gene is located on chromosome 13. As with BRCA1, women who inherit BRCA2 mutations have an 85% chance of developing breast cancer. Members of families with the abnormal BRCA2 gene also seem to be at greater risk for several other cancers including male breast cancer.

The BRCA1 and BRCA2 genes appear to code for the production of proteins that suppress tumor growth. If either gene pair is altered in such a way that they no longer code for the protein necessary to suppress growth, a tumor will form. The loss of gene function, however, is only one of a number of events that must take place before the tumor becomes invasive and metastasizes.

• obtaining detailed family history information, medical records and a lifestyle history
• documenting all cancer related diagnoses within the family
• analyzing the available information and classifying a person as having a low, moderate or high risk of breast and/or ovarian cancer
• providing risk assessment and counseling services
• discussing options for early detection and possible prevention

Individual breast cancer risks are calculated based on a person’s family history and population based risk prediction models.

Women who are found to be at high risk for breast cancer are also offered the option of DNA testing to look for changes in one of the breast cancer genes. Women who are at an increased risk for breast cancer are women with a family history of breast or ovarian cancer whose affected relative has any one of the following:

• a personal history of pre-menopausal onset of disease, or
• two primary tumors, either breast/breast or breast/ovarian, or
• at least one first or second degree relative with early onset (pre-menopausal) breast or ovarian cancer, or
• autosomal dominant inheritance of breast and/or ovarian cancer susceptibility based on pedigree analysis