"In the worst-case scenario, results from these tests may lead to unnecessary medical interventions or false reassurances and missed diagnoses." -- Kenneth Offit, MD, MPH, Chief, Clinical Genetics Service |
Previous genetic tests, such as those designed to look for mutations in the BRCA1 and BRCA2 genes -- which increase the risk for breast and ovarian cancers -- have been studied and validated in clinical trials conducted over many years. When an individual is found to have mutations in these genes, there is a very high risk of disease, which may be more than twenty-fold greater than an average person's risk of the disease. Clinical measures may be available, including: increased regular screening designed to catch the cancer early, when it is easiest to treat; chemoprevention clinical trials, which are experimental trials that use drugs in an attempt to prevent or delay the onset of cancer; and the surgical removal of an at-risk organ before cancer develops. Optimally, individuals will discuss all these options with either their healthcare provider or a trained genetics counselor. More recent genetic tests may detect only small increases in disease risk, and guidelines for prevention in this setting may be less clear.
Government Oversight of Genetic Testing
Unlike new drugs, which must undergo a rigorous review process administered by the Food and Drug Administration (FDA), genetic testing laboratories are not fully regulated by the FDA. Of the tests now being offered for more than 1,500 diseases, the most exacting type of laboratory evaluation, known as proficiency testing, may not be required. In early May, an expert panel reporting to the US Department of Health and Human Services cited the absence of evidence to support the usefulness of many of these tests. As a result of these findings, the panel's report goes on to recommend that all genetic tests be examined by the FDA and subject to their more rigorous proficiency testing.
Questions of Test Accuracy and Professional Guidance
Kenneth Offit, Chief of the Clinical Genetics Service at Memorial Sloan-Kettering, wrote a commentary in the March 19 special genomics issue of the Journal of the American Medical Association, making recommendations to help doctors and counselors as they consider offering these tests in clinical practice. In his commentary, Dr. Offit questions the scientific accuracy and medical usefulness of some of these tests, which have not been validated in forward-looking, or prospective, clinical studies.
"In the worst-case scenario," Dr. Offit says, "results from these tests may lead to unnecessary medical interventions or false reassurances and missed diagnoses."
Marketing the tests directly to individuals creates its own potential problems. "The direct-to-consumer aspect of these tests excludes guidance from healthcare professionals," he explains. As a result, he notes, individuals considering these tests may not have the resources necessary to make unbiased decisions about whether to proceed with genetic testing. Additionally, individuals receiving the results of self-ordered tests may not receive counseling, which can include a discussion of appropriate medical interventions for the prevention and early detection of any genetic disorders that are uncovered.
Dr. Offit concludes by recommending a more cautious approach to introducing these new "whole genome" tests, suggesting that the tests first be subjected to the same prospective clinical trials that were used to assess the psychosocial and medical effects of genetic testing for breast cancer risk a decade ago.
