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Genetic test may predict patients' response to cancer drugs

Last Updated May 29, 2015 7:08 PM EDT

After fighting colon cancer for 20 years, Kate Winnie's doctors told her she was out of options. "Anybody who has been at that, heard those words, it's a pretty scary place to be," she told CBS News.

Winnie, 54, has a genetic condition that makes the cells in her tumor mutate thousands of times. But patients with the so-called mismatch repair genes may respond well to immunotherapy drugs, researchers at Johns Hopkins have discovered.

"The idea here was we can give one of these medications that turned on the immune system and would that allow your immune system to attack your tumor and remove it or eliminate it," said Dr. Luis Diaz, an oncologist Johns Hopkins Kimmel Cancer Center.

In recent preliminary research, published in the New England Journal of Medicine, doctors gave the immunotherapy drug pembrolizumab (marketed as Keytruda) to about 30 patients living with colorectal cancer. The participants in the study had received previous therapies but were no longer responding to them.

"Patients who would only live a few weeks to months are now living up over a year with no signs of the tumor growing or coming back," Diaz said, "and we're pretty enthusiastic about that."

"They gave an immune boosting drug and they had unbelievable results - albeit in a small number of people," said CBS News chief medical correspondent Dr. Jon LaPook, who is also an internist and gastroenterologist at NYU Langone Medical Center. "I don't want to give false hope," he said, but "to me, it's very exciting."

An additional 25 patients with colon and rectal cancer who did not have the defective gene were also given the immunotherapy drug but failed to respond. This suggests the mismatch repair genes are a biomarker for the drug to work.

LaPook said only 15 to 20 percent of people with colon cancer have this particular mutation, so the treatment wouldn't be an option for everyone.

Winnie, who has been receiving the drug every two weeks for a year and a half, is one of the patients that has responded well. "The scans show that there is no active cancer," she said. "There is nothing that has changed dramatically. They call it stable, or that it's a little bit smaller than it was."

She also said she has more energy now than she has in the last 10 years.

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