Unique to Women
Genetic Testing and Inherited Risk
Breast cancer, like other cancers, develops when changes occur in genes in breast cells. In that sense, all breast cancer has a genetic element. But, “genetic” does not mean inherited. Only an estimated 5% to 10% of breast cancer cases result from an inherited genetic predisposition to the disease. In other words, more than 90% of all breast cancer cases result from factors that are not inherited and, in many cases, are unknown.
So far, researchers have found two genes linked with breast cancer—labeled BRCA1 and BRCA2—that everyone inherits in pairs: one from our mother and one from our father. When they function normally, they are supposed to stop the growth of cancerous cells in the breast. When both genes in a pair are damaged, they don’t work properly and cancer may develop. People who inherit a damaged BRCA1 or BRCA2 gene from one parent are at greater risk of developing breast cancer than people who inherit two normal genes.
Studies can estimate risk among large numbers of people who have an inherited mutation, but not the risk for an individual woman. Women with any BRCA mutation have about a 33% to 50% risk of developing cancer by age 50, and a 56% to 87% risk by age 70. Most of the research focuses on women with a strong family history of breast or ovarian cancer (several female relatives on one side who have breast and/or ovarian cancer before age 40, cancer in both breasts, and/or cases of male breast cancer).
Blood tests have been developed—and are now aggressively marketed commercially—that can identify BRCA1/2 gene mutations. But, a positive test result (having one of these mutations) does not mean that an individual will develop breast cancer. Nor does a negative test mean that a woman won’t develop breast cancer; it means only that her lifetime risk is the same as that of most other women in the industrialized world. And, there’s no way to tell how strong the connection is between the various mutations that exist and the risk of getting breast cancer, or how aggressive (or non-aggressive) the disease will be if it develops in a mutation carrier.
Should I Get a Genetic Test?
Genetic testing can cause substantial psychological distress and create a variety of problems for us and our families, whether it finds a mutation or doesn’t. Since very few doctors have received the training necessary to safely guide patients in making decisions related to genetic testing, anyone considering a test should first get in-depth counseling from a trained genetic counselor.
Such testing also raises concern about the possibility of discrimination. Much of the research on genetic risk of breast cancer focuses on the Ashkenazi Jewish population, creating a risk of discrimination based on religious or racial status. Not all states have laws to protect mutation carriers and their families against genetics-based discrimination in employment or insurance policies, and there is no federal law that guarantees legal protection to all. One federal law, the 1996 Health Insurance Portability and Accountability Act (HIPAA), prohibits the use of genetic information to exclude individuals from group health plans, limit coverage or charge an individual more for premiums. Other bills that would broaden legal protection related to use of genetic information are pending in the U.S. Congress.
Genetic testing should be considered only in limited circumstances. Those most likely to benefit from genetic testing are people who believe, based on family history, that they are mutation carriers and, if so, want to take some action to try to reduce their cancer risk. All genetic testing should be accompanied by complete information about benefits and risks, professional counseling, and comprehensive written informed consent. We need to approach genetic testing with extreme caution until science can tell us more about what the results mean and public policy can protect us from discrimination in employment, insurance coverage or other areas on the basis of genetic information.
What Can I Do If I Have a Genetic Mutation?
For women who test positive for a gene mutation, the choices for reducing the risk of developing breast cancer are limited. More frequent mammography screening is one option—finding cancer early enough to possibly treat it effectively. However, radiation exposure may pose dangers, particularly to women who carry may carry other genetic mutations such as the AT mutation. Also, young women’s breast tissue is denser, so what can be seen on a mammogram is limited until about age 40. Clinical breast exams are the more appropriate screening method for pre-menopausal women. Prophylactic mastectomy—surgical removal of the breasts—is another option for reducing risk, but even that drastic step, which reduces risk by 90%, does not completely guarantee that breast cancer will not develop. Drugs for “chemoprevention” are a third possibility, but not much is known about the effectiveness of this approach in carriers of breast cancer-related genetic mutations, and the side-effects of such drugs are far more likely to cause other problems than to prevent breast cancer.
Women at increased risk of cancer can find a wealth of resources at FORCE: Facing Our Risk of Cancer Empowered. To read a personal story of a woman who tested positive for BRCA1 and decided to have a prophylactic mastectomy, click here.
Written by: Our Bodies Ourselves staff and Barbara Brenner
Last revised: March 2005
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