New genetic test could predict response to chemotherapy

By Elizabeth Cohen
CNN Medical Correspondent

BALTIMORE, Maryland (CNN) -- Researchers touted a genetic test that can help predict whether brain tumor patients will respond to chemotherapy, in a study released Wednesday. "This is very exciting," said Dr. John Weinstein, senior research investigator at the National Cancer Institute. "This could help us individualize treatments for patients based on their genetic make up."

In the study, patients with and without a particular genetic trait called methylation received chemotherapy. Two-and-a-half years after treatment, about 75 percent of the patients with methylation of this gene were still alive, compared with 20 percent of patients who were unmethylated.

Methylation occurs when a methyl group -- a carbon atom with three hydrogens -- is attached to the DNA in a tumor. Methylation turns off a process that makes tumors less receptive to chemotherapy with carmustine, the most commonly used chemotherapy for gliomas, a type of brain tumor. When tumors are unmethylated, this process stays in place and tumors are less responsive to chemotherapy.

Knowing this, patients with unmethylated tumors "could be spared the considerable toxicity of carmustine and could instead be given an agent more likely to be effective against the tumor," Dr. Weinstein wrote in an editorial in The New England Journal of Medicine, where the study was published.

The study was done at Johns Hopkins University and the Clinica Universitaria in Pamplona, Spain.

Scientists are already studying drugs that try to make unmethylated tumors behave more like methylated tumors, according to Dr. Richard Kaplan at the NCI's clinical investigations branch.

More studies would need to be done before doctors would start routinely testing patients for methylation, cancer experts said this week, but if the results are duplicated, they could perhaps be applied to other cancers besides gliomas.

The experts said the study is exciting because it's part of a new way of looking at cancer.

"Traditionally what's been done is to look at the way the tumor looks -- how big it is, how deep it is -- and then look at it under a microscope to see what the cells look like. But this is looking at a tumor on the molecular level, which is thousands of times smaller than the cellular level," Dr. Weinstein said.

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American Cancer Society
The Johns Hopkins Brain Tumor Radiosurgery
National Institutes of Health: Brain Tumors

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