Blood Screening Trumps Biopsy in Cancer Mutation Hunt

A simple blood sample turned up cancer-causing mutations more frequently than a tumor biopsy in a study that suggests the approach could help deliver a clearer picture of the disease and better tailor patients’ treatments.

In a study of Bayer AG’s drug Stivarga, researchers analyzed tissue and blood samples from patients with gastrointestinal stromal tumors, or GIST, to find cancer-driving mutations. They found that blood samples were more likely to reveal them than biopsies, in results presented today at the American Association for Cancer Research meeting in Washington.

As cancer treatments increasingly home in on known genetic causes of the disease, researchers need better tools to determine just what mutations each patient has, said George Demetri, director of the Ludwig Center at Dana-Farber Cancer Institute and Harvard Medical School, who led the trial. Samples taken from tumors may not reveal all the underlying mutations at once, he said in an interview.

“A biopsy is by definition a subset of the tumor cells,” Tyler Jacks, director of the Koch Institute for Integrative Cancer Research at the Massachusetts Institute of Technology, said in a telephone interview. He wasn’t associated with the research. “What’s cool about this idea is the use of the blood sample as a surrogate to what’s happening in the tumor.”

The screen, called BEAMing technology, is sensitive enough to detect even rare mutations circulating in the blood stream in the form of free DNA, genetic material shed from tumors. Demetri said he expects the testing technology could become a standard part of caring for cancer patients within five to 10 years.

Stivarga Trial

The analysis was done as part of Leverkusen, Germany-based Bayer’s trial of Stivarga, a cancer therapy approved in February for GIST and last year for colorectal cancer. Researchers took DNA from tumor tissue and analyzed it for mutations in two genes known to drive cancer-causing proteins targeted by Bayer’s drug and medicines from Pfizer Inc. and Novartis AG, Sutent and Gleevec.

Stivarga is approved for use in GIST after patients’ cancer has stopped responding to Sutent and Gleevec. Bayer jointly promotes Stivarga with Onyx Pharmaceuticals Inc. In the study, researchers took blood samples from patients once their cancer had progressed and analyzed them for mutations, including so-called secondary mutations that cause resistance to those drugs.

They found secondary mutations in 48 percent of blood samples, versus 12 percent of tissue samples.

“The problem for the last decade of research is when you take out one tumor and sample one corner of the tumor and then sample another, you may see two different mutations in that same tumor,” Demetri said in an interview. “What we were looking for was technology that, with a simple blood test, we’d be able to sample all the mutated DNA in a person’s body.”

Technology Limitations

The technology has some limitations, Demetri said. It detects expected mutations, while is unable to turn up unknown drivers of cancer. Newer versions of the technology are being worked on now that would enable researchers to seek out unidentified cancer-causing mutations, which could be helpful for drug development.

The test may help identify which patients should receive which drugs, Demetri said, enabling some to skip treatments that won’t work for them or others to be given just the right therapy for the driver of their cancer.

“Dynamic monitoring and understanding what’s happening to the tumor over time, how it’s evolving, is important,” Jacks said. “This technology allows you to do that.”

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