By Diane Allingham-Hawkins, PhD, FCCMG, FACMG, Director of the Hayes Genetic Test Evaluation Program
Did you read the article series in the New York Times about genetic testing in patients with cancer? (Genetic Gamble – New Approaches to Fighting Cancer) One of the strategies discussed in the well-researched three-part series was whole-genome sequencing, a personalized medicine approach for patients with cancer.
Personalized medicine holds tremendous promise for improving outcomes in people with cancer but as this series clearly demonstrates, these genetic tests are not ready for widespread use. Whole-genome sequencing is expensive, time consuming, and out of reach for most patients. The patients profiled were fortunate to have access to virtually unlimited resources because of their personal relationships with experts in the field. Keep in mind, too, that only a handful of case reports for the use of whole-genome sequencing in people with cancer have been published in the scientific literature. There is currently no evidence that such testing improves clinical outcomes for patients with cancer.
Let’s look more closely at whole-genome sequencing. The complex process seeks to determine the complete DNA sequence of an individual’s genome by sequencing the entire DNA contained in the person’s chromosomes. When applied to patients with cancer, whole-genome sequencing analyzes healthy cells as well as cancer cells for comparison. Ideally, if the results show genetic changes in the cancer cells that are responsible for cancer growth, then targeted therapies can be administered to stop or slow the progression of cancer. Some of these therapies may be FDA-approved for this application. If they are not, then it is perfectly legal to use them off label. However, the off-label use of any drug is risky at best and dangerous at worst. Although the two patients profiled in this series experienced some benefit from taking drugs that were FDA approved for different forms of cancer, how many patients may die trying?
Whole-genome sequencing is not the panacea. Yes, it appears to be leading us in the right direction as we learn more about the genetic basis of cancer. But at the present time it is a costly, difficult process. The human genome comprises 3 billion bases or “letters” of DNA sequence and there are millions of differences, even between two healthy individuals. Identifying which genetic variants are important to the development of cancer in any given person is not easy.
I have no doubt that there will come a time when personalized medicine is a safe, proven, and affordable option for all patients with cancer. However, until the evidence shows that strategies such as whole-genome sequencing improve patient outcomes, we should proceed cautiously.