Hereditary Breast Cancer Testing
Who Should Be Tested and How Should Results be Interpreted?
Nov 14, 2008
Deciding whether or not testing is the right choice entails understanding what the test is and what it can and cannot determine. The first gene associated with breast cancer – BRCA1 – was identified in 1994 on chromosome 17, according to the National Human Genome Research Institute. A year later, a second gene – BRCA2 – was discovered on chromosome 13. Since then, nearly 2,000 mutations have been identified on the genes, according to the Mayo Clinic online article, “Genetic Testing for Breast Cancer: What the Results Mean.” But, not all of these mutations carry the same risk of cancer and having a mutated BRCA gene does not mean a woman will contract breast or ovarian cancer.
In fact, not all hereditary breasts cancers are caused by BRCA1 and BRCA2. Researchers now believe that at least half of the hereditary breast cancers are not linked to these genes and that the remaining cases are not caused by another single, unidentified gene, but rather by many genes.
How Does a Woman Know Whether to be Tested?
When there is a strong family history of breast cancer, hereditary breast cancer is considered a bigger risk. A strong family history means disease occurrences in at least three first or second-degree relatives (sisters, mothers, aunts). The only tests currently available are DNA tests to determine whether a woman in such a high-risk family has a genetic mutation in the BRCA1 or BRCA2 genes.
What Does a Positive Test Result Mean?
Once a woman decides that hereditary breast cancer testing is needed, what do those test results mean? Positive results indicate that there is a mutation in one of the breast cancer genes, according to the MayoClinic.com article. This puts a woman at a much higher risk of developing breast or ovarian cancer compared with someone at average risk. The Mayo Clinic suggests several risk-reducing options:
- Monitoring: Clinical breast exams and mammograms at least once a year, as well as monthly breast self-examination. These tests are suggested for everyone – those at high risk and those who are not.
- Medication: Drugs used to reduce the risk of cancer, also called chemoprevention. Tamoxifen administered for five years is the current suggested regimen most commonly used to reduce breast cancer risk in high-risk women. Also used is Raloxifene, a drug that has been used up until now primarily for preventing and treating osteoporosis. It has been found to be as effective as tamoxifen.
- Preventive Surgery: Prophylactic mastectomy surgery is performed. This is the removal of healthy breast tissue and can reduce the risk of breast cancer by about 90 percent. However, preventive surgery doesn’t eliminate all cancer risk. Cancer might still develop in the tissue that wasn’t removed.
What Does a Negative Test Result Mean?
Negative test results are only truly negative if the test finds that a woman doesn’t carry a specific BRCA mutation already identified in a relative. In that instance, it means that a woman’s risk of breast and ovarian cancer is the same as that of the general population. In any other situation, a negative result means that a woman may still be at high risk of hereditary breast cancer if her family carries a high-risk gene mutation that has not yet been identified or the test was unable to detect her family’s gene mutation.
Sources:
“Learning About Breast Cancer” at genome.gov (National Human Genome Research Institute)
“Genetic Testing for Breast Cancer: What the Results Mean” at MayoClinic.com
Links
The Genetics Home Reference at the National Library of Medicine provides a summary FAQ on breast cancer.
Helpful articles such as Genetic Testing for Breast Cancer Risk: It’s Your Choice, Genetics of Breast and Ovarian Cancer, and Breast Cancer: Prevention, Genetics, Causes are available at cancer.gov.
Comprehensive resource list of online information about breast and ovarian cancer genetics is available from NOAH (New York Online Access to Health).
