Genetic testing for breast cancer: not a test for every woman
I have read a lot lately about a genetic test that can predict if you are predisposed to breast cancer. How can I determine if I will benefit from taking the test?
Genetic testing for breast cancer and other life-threatening diseases is an extremely controversial issue. It raises questions that go far beyond a clinical diagnosis of the disease, involving emotional, legal, and ethical issues. Since about one in eight American women will experience this illness in her lifetime, it is a topic of importance to health professionals, ethicists, breast cancer patients, advocacy groups, and women's organizations.
Two types of tests can be performed to determine an individual's susceptibility to breast cancer, according to Carol Rosenberg, M.D., an assistant professor of medicine at Boston University School of Medicine and a staff physician at Boston Medical Center. The most common is a genetic test that examines an individual's DNA -- the molecules that contain the human genetic code -- to determine if specific abnormalities would lead to a dysfunctional structural protein encoded by the mutated DNA. This dysfunctional protein would act in a way that contributes to breast cancer development. The other test, called the protein truncation test, examines the protein directly; it is being developed, but is not currently available.
Only two genes responsible for breast cancer have been detected unequivocally, and the tests thus far have been developed only to detect abnormalities in these two genes. There may be other, unidentified genes, however, that also play a role in breast cancer. "The genes that have so far been identified," says Rosenberg, "are thought to account for only a small fraction of breast cancer cases -- about 5 to 10 percent."
Rosenberg says there are no absolute factors that determine who is a candidate for such testing. However, women with a family history of breast cancer or who are members of certain ethnic groups (primarily homogeneous populations like Ashkenazi Jews or French Canadians) that have a higher incidence of specific genetic abnormalities are considered prime candidates for genetic testing.
"This is not a test for every woman," says Rosenberg. "It is not a test you just go to your doctor for to determine your susceptibility to breast cancer. If we discover additional genes that are responsible for breast cancer, then this test will become available to a broader population of women. But for the foreseeable future, it will remain only for those women in specific high-risk groups, based on family history."
Genetic tests are not administered in a physician's office. Rather, an individual must either be enrolled in a research study and meet certain study criteria or have it conducted by one of several commercial companies with tests on the market.
One of the major issues surrounding genetic testing for breast cancer and other diseases is what course to take if there is an indication that breast cancer may develop, but there is no clinical diagnosis of disease. Rosenberg says positive results could lead to aggressive and perhaps unnecessary responses such as prophylactic mastectomy. On the other hand, women with negative results may mistakenly assume that they have no risk for breast cancer. Rosenberg says genetic counseling should be available to all women who undergo genetic testing and their families to discuss the test and its implications.
Despite the ethical and legal dilemmas that genetic testing may pose, it might have certain clinical benefits, perhaps including prevention of the disease. "If nothing else," says Rosenberg, "genetic testing may lead to increased vigilance for screening for early detection."
Advocates, like the Genetics and IVF Institute in Virginia, contend that "genetic predisposition testing will play a major role in turning the tide in the war against breast cancer" by identifying high-risk individuals, increasing surveillance, and providing people with important information about their health.
Notwithstanding these claims, says Rosenberg, most of the medical community remains uncertain about the role genetic testing will play in the fight against breast cancer. "We are still not certain what normal means for genes, much less what abnormal means," she says. "And the genes we have identified cover only a small portion of all breast cancer cases. There is still a lot more work that needs to be done before genetic testing becomes widespread and readily available."
"Health Matters" is written in cooperation with staff members of Boston Medical Center. For more information on genetic testing for breast cancer or other health issues, call 638-6767.