The drugs were melanoma treatment Yervoy, already on the market, and the company's experimental drug nivolumab.

In the Bristol-Myers study, using a two-drug combination that targets the immune system resulted in "rapid and deep tumor regressions" in nearly one-third of 52 skin cancer patients treated with the combination, researchers said.

Scientists have been trying for decades to understand why the body's immune system didn't see cancer cells as the enemy and attack them.

The combination was more efficient than each drug given alone, said Jedd Wolchok, an oncologist at Memorial Sloan-Kettering Cancer Center in New York, who led that study.

Though the studies are small, the results reflect rapidly growing conviction that immunotherapy is the next big front in the war on cancer.

Recent discoveries revealed that tumors are adept at cloaking themselves by hijacking the body's own mechanism for preventing the system's T-cells, the infection-and disease-fighting cells of the immune system, from running amok against healthy tissues.

Merck & Co., for instance, is also moving quickly with a candidate that targets the immune system.

Side effects of the drugs include inflammation associated with the immune system's activation against tumors, but researchers said they were either resolved or were treated without serious consequence.

Based on the results, Roche is planning to launch a late-stage trial of its PD-L1 inhibitor in lung-cancer patients, while Bristol-Myers is moving its combination regimen into late-phase studies as well. Thank you.