Personalizing Cancer Treatment With Genetic Tests Can Be Tricky
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These days, doctors have the ability to perform a detailed genetic test on tumors to help guide cancer treatment. Tens of thousands of patients now get these genomic tests every year. Sometimes the results point to a specific treatment, but often they're ambiguous. New research suggests a way to make these expensive tests more useful. Here's NPR's Richard Harris.
RICHARD HARRIS, BYLINE: Cancer doctors use all sorts of tests, from scans to biopsies, to help diagnose the disease and settle on the best drugs to use.
VICTOR VELCULESCU: But more and more they're using genomic analyses to determine what sort of therapy a cancer patient should receive.
HARRIS: Victor Velculescu is a cancer researcher at Johns Hopkins. He also started a company that scans hundreds or even thousands of genes looking for mutations that may be related to cancer. He and his colleagues have just published a study in Science Translational Medicine looking at how effective these tests are if they simply look at a person's tumor cells and don't compare that to a person's healthy tissue.
VELCULESCU: What we found is that you essentially get a lot of inaccurate information.
HARRIS: These genomic tests pick up a huge number of mutations, but most of those mutations aren't relevant, and it's often not easy to tell which mutations matter and which don't. The consequences of getting this wrong could be significant.
VELCULESCU: You can imagine patients being placed on a particular therapy without the - you know, with all the side effects of that therapy but without any of the benefits. You can imagine that that ends up preventing the patient from getting the right therapy. And then finally, there's the additional costs of having these therapies that aren't really useful in any way.
HARRIS: Dr. Velculescu argues that these tests would provide better results if they compared tumor tissue to an individual's normal tissue. That way doctors can single out mutations clearly linked to the cancer. That's, in fact, what his company does, so he has an economic interest in making this argument. Other scientists do agree with his fundamental point, but they also say that existing tests are actually quite accurate when used appropriately.
Dr. Neal Lindeman runs these tests at the Dana Farber Cancer Center and Brigham and Women's Hospital. He says the genomic tests reliably identify mutations that are unambiguously linked to certain cancers.
NEAL LINDEMAN: And those are the ones that are used clinically for making decisions about what to do for a patient and what's the optimal way to take care of that patient.
HARRIS: So do you think people are being inappropriately treated right now based on incorrect genome analysis of their cancers?
LINDEMAN: No, I do not. I think that there's enthusiasm that may lead people to go into clinical trials with incomplete information. But as far as therapies that are approved by the food and drug administrations, I do not believe that this is an error.
HARRIS: Here's why people may end up in an inappropriate clinical trial based on a genomic test. Doctors may see a mutation in a particular gene and guess that it's related to the cancer without really knowing. It's here that a comparison test with normal tissue would really add clarity by identifying mutations that don't really matter. At the moment, many companies that perform these genomic tests don't run that additional expensive comparison. Dr. Vince Miller, chief medical officer at Foundation Medicine, says instead, his company sorts the results of these tests so doctors can distinguish what's certain and what's speculative.
VINCE MILLER: I have seen reports from other vendors or institutions where they just throw everything together. And that does create this potential where one could be treating the patient on the basis of something that is not a cancer-driving alteration. But we clearly make that distinction.
HARRIS: And there's room for this confusion because this booming industry is not tightly regulated by the Food and Drug Administration. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.