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"This trial shows that pembrolizumab used alone improves survival as opposed to chemotherapy," said lead researcher Dr. Gilberto Lopes, a medical oncologist with the Sylvester Comprehensive Cancer Center at the University of Miami Health System.
But while Keytruda works better than chemotherapy, the combination of the two is likely to be the best first choice for treatment of lung cancer, Lopes added.
"We do believe based on a study presented about a month ago that the combination of chemotherapy plus pembrolizumab probably is better than pembrolizumab alone," Lopes said. "What we likely will see as the new standard of care is for us to combine both drugs."
Keytruda fights cancer by "taking the brakes away from the immune system so our own defense cells can recognize cancer cells and kill them," Lopes explained.
The drug has also worked well against other cancers. When former President Jimmy Carter was diagnosed with melanoma that had spread to his brain several years ago, it was Keytruda that threw the cancer into remission by curtailing the action of a protein known as PD-L1.
PD-L1 is found on cancer cells, and it essentially shoos away the immune system, fooling it into thinking that cancerous tissue is normal and healthy. Keytruda blocks that interference, allowing killer immune cells to find and destroy the cancer.
Usually, tumors with larger amounts of PD-L1 respond better to treatment with pembrolizumab. But some studies have shown that similar immunotherapies also have been effective against tumors with little or no detectable PD-L1, the researchers said in background notes.
To see just how effective pembrolizumab can be across the board, Lopes and his colleagues randomly assigned 1,274 patients with advanced lung cancer to receive either pembrolizumab or chemotherapy. Average follow-up time was almost 13 months.
The researchers found that anyone who received pembrolizumab had longer average survival than those who underwent chemotherapy, about 16.7 months versus 12 months.
But the benefits of pembrolizumab increased with the amount of PD-L1 expression in lung tumors:
- Patients with PD-L1 in half of their tumors experienced 20 months average survival on pembrolizumab, compared to 12 months with chemotherapy.
- Those with PD-L1 in 20 percent of tumors had 17.7 months average survival with pembrolizumab, compared with 13 months for chemotherapy.
"For all the three groups we studied, pembrolizumab led to longer survival and higher overall survival rates than chemotherapy alone," Lopes said.
The immunotherapy also proved to be a milder treatment than chemo. Only 18 percent of patients reported severe side effects with pembrolizumab, compared with 41 percent of patients on chemotherapy.
This would make pembrolizumab a strong option for older and sicker lung cancer patients who can't safely handle the strain caused by chemo, said ASCO President Dr. Bruce Johnson, chief clinical research officer at the Dana-Farber Cancer Institute in Boston.
"You can give these therapies to people who are not feeling particularly well, because for most of the people it doesn't have the kind of side effects that come with chemotherapy," Johnson said.
Future studies will need to focus on how to best decide the right treatment for each patient, Lopes said.
"The big question now is who are the patients who might benefit from this alone, and those persons who might need pembrolizumab and chemotherapy to have the best response," Lopes said.
Keytruda costs about $10,000 a month, Lopes said, in line with other newer cancer drugs but more pricey than older chemotherapy drugs.
The study, funded by Keytruda manufacturer Merck, was scheduled for presentation Sunday at ASCO's annual meeting, in Chicago. Because they have yet to be published in a peer-reviewed medical journal, the findings should be considered preliminary.
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SOURCES: Gilberto Lopes, M.D., medical oncologist, Sylvester Comprehensive Cancer Center, University of Miami Health System; Bruce Johnson, M.D., president, American Society of Clinical Oncology, and chief clinical research officer, Dana-Farber Cancer Institute, Boston; June 3, 2018, presentation, American Society of Clinical Oncology annual meeting, Chicago