CHICAGO – They’re not cures, but two novel drugs produced unprecedented gains in survival in separate studies of people with melanoma, the deadliest form of skin cancer, doctors reported Sunday.

In one study, an experimental drug showed so much benefit so quickly in people with advanced disease that those getting a comparison drug were allowed to switch after just a few months.

The drug, vemurafenib, targets a gene mutation found in about half of all melanomas. The drug is being developed by Genentech, part of Swiss-based Roche, and Plexxikon Inc., part of the Daiichi Sankyo Group of Japan.

The second study tested Bristol-Myers Squibb Co.’s Yervoy, a just-approved medicine for newly diagnosed melanoma patients, and found it nearly doubled the number who survived at least three years.

The new studies were presented Sunday at the American Society of Clinical Oncology’s annual meeting in Chicago and published online by the New England Journal of Medicine.

Melanoma is on the rise. There were 68,000 new cases and 8,700 deaths from it in the United States last year, the American Cancer Society estimates. Only two drugs had been approved to treat it, with limited effectiveness, until Yervoy, an immune-system therapy, won approval in March.

The experimental drug, vemurafenib, is aimed at a specific gene mutation, making it the first so-called targeted therapy for the disease. The drug got attention when a whopping 70 percent of those with the mutation responded to it in early safety testing.

The new study, led by Dr. Paul Chapman of Memorial Sloan-Kettering Cancer Center in New York, was the key test of its safety and effectiveness.

It involved 675 patients around the world with inoperable, advanced melanoma and the gene mutation. They received vemurafenib pills twice a day or infusions every three weeks of the chemotherapy drug dacarbazine.

After six months, 84 percent of people on vemurafenib were alive versus 64 percent of the others.

Less than 10 percent on the drug suffered serious side effects — mostly skin rashes, joint pain, fatigue, diarrhea and hair loss. About 18 percent of patients developed a less serious form of skin cancer. More than a third needed their dose adjusted because of side effects.

“Within 72 hours, their symptoms improve, pain medicines can be reduced,” said Dr. Lynn Schuchter, of the University of Pennsylvania’s Abramson Cancer Center.