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Genetic Testing

Updated September 27, 2010

Breast cancer develops when abnormal genes that control cell growth prompt cells in the breast to grow out of control. The genes can be defective from birth, or they can undergo changes during your lifetime.

About 5 percent to 10 percent of all breast cancers are caused by defective genes inherited from one’s parents; all other breast cancers are caused by other risks which may be inherited or environmental.

Researchers have found two genes with inherited mutations linked to an increased risk of breast cancer: BRCA1 and BRCA2 (BRCA stands for BReast CAncer).

BRCA1 and BRCA2 Testing

If you inherited a BRCA1 or BRCA2 mutation, your lifetime risk of developing breast cancer is 60 percent to 80 percent, compared to about 13 percent in the general population. A BRCAAnalysis blood test or a new test called BRCAAnalysis Rearrangement Test (BART) can find both these mutations. Many insurers will cover genetic testing.

If you have a BRCA1 mutation, you have a 30 percent to 45 percent lifetime risk of developing ovarian cancer. Between 75 percent to 90 percent of BRCA1 associated breast cancers will be estrogen receptor-negative.

If you have a BRCA2 mutation, you have a 10 percent to 20 percent lifetime risk of developing ovarian cancer. BRCA2 mutations are more likely to cause estrogen receptor-positive cancers, about 65 percent to 80 percent of the time.

The results of a genetic test usually are sent to the doctor who ordered the test within four to five weeks of the test date. If your result is positive, you have a genetic mutation that’s known to increase breast cancer and related cancer risks. If your result is negative, the test did not find a genetic mutation associated with breast cancer risk in your family. If you have a strong family history of breast cancer, you may still have an increased risk.

Making Decisions

Surveillance, or close monitoring, is one acceptable option for women with BRCA mutations. MRI screening is now standard for those at high risk of developing inherited breast cancer.

Chemoprevention, or using a medicine like tamoxifen to reduce risk, can lessen your chances of developing estrogen receptor-positive breast cancer. Also available is preventive (prophylactic) mastectomy, which means removing a healthy breast to lower the risk of cancer developing in the future.

Another option is preventive salpingo oophorectomy, which means removing the ovaries and fallopian tubes. In premenopausal women with BRCA mutations, this can reduce the risk of developing ovarian cancer by more than 90 percent. This surgery also lowers the risk of BRCA2-related breast cancer significantly.

Genetic Counseling

If you believe you may have inherited a genetic mutation, a genetic counselor can help interpret your family and personal health histories to determine whether you need genetic testing.

Your genetic counselor will ask about your risk factors for developing breast cancer. This person can explain the risks, benefits and limitations of genetic testing and how test results might impact prevention and treatment options. They also can help you make a decision about whether genetic testing would be beneficial to you and your family.

Read more about genetic testing and the providers who helped us write this page in our Insight newsletter from Summer 2009.