CHICAGO - Researchers have scored the first big win against melanoma, the deadliest form of skin cancer. An experimental drug significantly improved survival in a major study of people with very advanced disease.

The results, reported Saturday at the American Society of Clinical Oncology's annual conference in Chicago, left doctors elated.

"We have not had any therapy that has prolonged survival" until now, said Lynn Schuchter, a physician at the Abramson Cancer Center at the University of Pennsylvania, a skin-cancer specialist with no role in the study or ties to the drug's maker, Bristol-Myers Squibb Co.

The drug, ipilimumab (ip-ee-LIM-uh-mab), works by helping the immune system fight tumors. The Food and Drug Administration has pledged a quick review, and doctors think the drug could be available by the end of this year.

"People are going to have a lot of hope and want this drug, and it's not on their doctors' shelves," though some may be able to get it through special programs directly from Bristol-Myers, said Schuchter.

Melanoma is the most serious form of skin cancer. Last year in the United States, about 68,720 new cases were diagnosed, and 8,650 people died from the disease. Worldwide, more than 50,000 people a year die of melanoma.

"The incidence is rising faster than any other cancer," said one of the study's leaders, Stephen Hodi, a doctor at the Dana-Farber Cancer Institute in Boston. "When it spreads to vital organs, it's almost always fatal."

The study involved 676 people around the world with advanced, inoperable melanoma who had already tried other treatments - a very grim situation. They were given one of three treatments: ipilimumab by itself, with another immune-stimulating treatment, or the immune-stimulating treatment alone.

After two years, 24 percent of those given the drug alone or in combination were alive, vs. 14 percent of those given just the immune-stimulating treatment.

Average survival was 10 months with ipilimumab vs. just over six months for the others - a 67 percent improvement in survival for those on the drug, said another of the study's leaders, Steven O'Day, a physician with the Angeles Clinic and Research Institute in Los Angeles.

Doctors hope the drug can provide more benefit if given earlier in the disease and to patients who are less sick.

Ten percent to 15 percent of patients on ipilimumab had serious side effects related to the drug's actions on the immune system. Most were treatable with high doses of steroids, but 14 deaths were thought to be related to the treatment. That's still far fewer than deaths from the cancer.

The study was funded by Bristol-Myers and Medarex Inc., a company that codeveloped the drug and was bought last year by Bristol-Myers. A spokeswoman said Bristol-Myers had not yet set a price for the drug, but similar treatments for other cancers cost several thousand dollars a month or more.

Results were published online by the New England Journal of Medicine.