Philadelphia ? Giving patients with advanced melanoma two Bristol-Myers drugs that work differently held the deadly skin cancer at bay far longer than just one, though the combination’s considerable increase in serious side effects raises concerns about how much patients can endure.

A study of 142 patients not treated previously found combining Yervoy and Opdivo, which mobilize the body’s immune system to target cancer cells, greatly boosted survival over giving Yervoy alone. The company said the combo also was better than Odivo alone, based on a prior study.

In the midstage study, presented Monday at the American Association for Cancer Research conference in Philadelphia, tumors were eliminated in 22 percent of those getting both medicines but in none receiving only Yervoy.

Yervoy and Opdivo together reduced chances of death or cancer progressing by 60 percent, compared to Yervoy alone. In the Yervoy-only group, death or worsening of cancer occurred after 4 1/2 months on average. That average hasn’t been determined yet in the combo group, in which some patients remained in treatment at 15 months.

“It’s reassuring and adds really important information about (the effects) of giving these two agents together,” said Dr. Lynn Schuchter, chief of hematology/oncology at University of Pennsylvania’s Abramson Cancer Center.

Melanoma, the deadliest skin cancer, each year kills about 10,000 Americans and strikes about 73,000.

In the study, funded by Bristol-Myers Squibb Co. of New York, two-third of participants got both drugs and the rest just Yervoy, with treatment continuing until tumors resumed growing or side effects became intolerable. Three patients, all getting the combination, died. The results for the combo were a little better than in an earlier, smaller study.

In the new study, compared to those only given Yervoy, three times as many patients getting both drugs — 47 percent — quit the study because of side effects, including liver problems, colitis and severe diarrhea. The company said other medicines eventually stopped those in most participants, and two-thirds benefited from the combination even after dropping out.

Schuchter, who was not involved in the study, said she’s not convinced patients need to take two such potent cancer drugs simultaneously. She noted results of other research, expected to be released in the near future, may clarify what’s best.

There’s one school of thought that doctors should fire both guns at once, because Yervoy and Opdivo helped mobilize the immune system to fight cancer in different ways. Others favor giving Yervoy and Opdivo sequentially.

A key factor in doctors’ decisions likely will be whether the patient is strong enough to withstand side effects of both drugs.

Yervoy costs about $131,000 for a full course of four treatments. Opdivo, which was given as long as patients benefited, costs about $12,500 per month.