Genetic Testing for Cancer Can Help … and Confuse

The more we know about genetics, the better we get at diagnosing and treating disease. At least that’s the way it’s supposed to work. But the line from someone’s genetic profile to a personalized cancer treatment is hardly straight.

Genomic tests look for thousands of gene mutations that might cause or promote cancer growth, but such scans uncover not only problematic mutations, but some that might be harmless.

So, according to a story on NPR, the routine genetic tests a doctor orders to help focus treatment on someone’s tumor can give results that fall into the “too much information” category. They can be ambiguous, and ambiguity is not your friend when targeting a tumor.

But if science is complicated, and invariably it is, a study in Science Translational Medicine indicates there’s a way to make the expensive genetic tests more useful for treating cancer.

The researchers found that about half of patients whose tumors are subjected to genetic testing get results that potentially are misleading. The consequences of misinterpreting the results could be severe.

As the lead researcher told NPR, “You can imagine patients being placed on a particular therapy, with all the side effects of that therapy but without any of the benefits,” said Dr. Victor Velculescu, a professor of oncology and pathology and co-director of cancer biology at the Johns Hopkins Kimmel Cancer Center. “You can imagine that it prevents the patient from getting the right therapy. And then, finally, there are the additional costs of having therapies that aren’t really useful in any way.”

Velculescu’s team believes that there’s a way to refine genetic test results: Study the DNA of the patient’s healthy tissue at the same time the tumor is sampled. It’s a contrast-and-compare approach that, the researchers believe, should help doctors tell the difference between mutations that are unique to the cancer and those that aren’t.

As NPR noted, Velculescu isn’t purely a scientist in this field – he is co-founder of a company that performs these cell comparison tests. So he has an economic interest in this protocol. Still, he’s not the only scientist that supports comparison testing.

And the tests generally do appear to be accurate when properly performed. They reliably identify mutations linked to certain cancers, “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,” Dr. Neal Lindeman told NPR. He’s a Harvard University pathology professor who runs a cancer genome program at Dana Farber Cancer Center and Brigham and Women’s Hospital.

Lindeman also said that genetic tests pick up a lot of ambiguous information that can lead people into clinical trials that are wrong for them. So comparison testing with healthy tissue could help avoid this by focusing only on the mutated genes more likely to contribute to the cancer.

Today, according to NPR, many companies that perform these genomic tests don’t run the additional comparison. The genome test by itself can cost more than $5,000, and adding another to analyze normal tissue would increase that cost substantially, which insurance often won’t cover.

Some companies sort genetic testing results to enable doctors to easily distinguish between clear and speculative results, but others don’t. As one doctor told NPR, “that does create this potential where one could be treating the patient on the basis of something that is not a cancer-driving alteration.”

Genetic testing is a wonderful tool, but because the cancer genomics industry is not tightly regulated by the FDA, providers and patients are often on their own to sort out the good, the possibly good, the extraneous and the potentially harmful.

If you are advised to undergo genetic testing as a way to target your treatment for cancer, find out which company is doing the testing, and ask if any measures are taken for sorting out all the results among the known, unknown and potentially harmful. Ask about comparison testing of tumor and healthy tissue.

You probably won’t get a clear, obvious answer to how best to treat your disease, but at least you’ll have information to help you and your doctor make as informed a decision as possible.

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