By Diane Allingham-Hawkins, PhD, FCCMG, FACMG, Senior Director, Genetic Test Evaluation Program
In the more than 25 years that I have been active in the field of genetics, personalized medicine has always been a primary goal, one that always seems that it should be achievable but continues to be just out of reach. Personalized medicine refers to using a person’s genetic information to guide their medical care, including prevention, diagnosis and treatment of disease. Although the concept is simple—sequence someone’s genes and then use that information when making medical decisions—the reality is much more complex and progress has been slow.
There is definitely more awareness of the impact of genes on drug response. A recent report from the Personalized Medicine Coalition reported that the number of drugs with pharmacogenetic information on the label increased from 4 at the start of the Human Genome Project in 1990 to 104 in 2013. It is important to note, however, that inclusion of such information on the drug label does not demonstrate that knowing genetic information has been proven to improve outcomes in patients taking the drug. The Food and Drug Administration (FDA) does not require evidence of clinical utility when deciding if such information should be included on the drug label.
There are some great examples of how knowing genetic information can improve outcomes for patients. In malignant melanoma, patients whose tumors have the p.Val600Glu variant in the BRAF gene respond much better to treatment with vemurafenib than patients without the variant. In metastatic colorectal cancer, patients whose tumors have variants in the KRAS gene are much less likely to respond to treatment with cetuximab or panitumumab than patients with no variants. Consequently, knowing this information allows patients and their healthcare providers to make informed decisions about treatment options.
Unfortunately, most cases are not so clear cut and studies show inconsistent results with respect to the cause and effect relationship between a drug response or adverse event and specific genetic variants. The case of warfarin pharmacogenetics is an excellent example. Early studies suggested that information about variants in the CYP2C9 and VKORC1 genes could help with more accurate dosing with warfarin, a drug that is associated with a significant number of adverse events annually. As data have accumulated, however, it is clear that warfarin metabolism is more complex than anticipated and studies of the benefits of incorporating genetic information into dosing have yielded conflicting results.
So, is truly personalized medicine around the corner? Not yet. Much more research is needed to establish not only an association between certain genetic variants and drug metabolism but also to demonstrate that knowing this association can lead to changes in patient care that improve outcomes. Hayes will continue to monitor the progress in this exciting field and provide independent and unbiased evaluations to assist our clients in making informed decisions.