But with patients already begging doctors for the drug, it seemed unlikely that anyone would join a trial with only a 50-50 chance of getting PLX4032 once it was already on the market. Unless the trial was conducted before approval, it seemed, there would be no chance to get definitive data on its effectiveness.

Some melanoma specialists familiar with the drug would have traded the data for faster access to the drug. “I know all that I need to know based on the results we already have,” said Dr. Keith Flaherty of Massachusetts General Hospital, who led the early clinical testing. “My use of this drug is not going to be informed by testing it against a drug we all hate and would rather never give a dose of again in our lives.”

The standard chemotherapy used in melanoma, dacarbazine, slowed tumor growth in 15 percent of patients for an average of two months. By contrast, PLX4032 had halted tumor growth in 81 percent of patients for an average of eight.

It was conceivable that when the cancer started up again, it would progress much faster in patients who had taken the new drug, wiping out any extra time they might have gained. But even if so, many doctors believed that if the drug provided relief by shrinking tumors  like the one Mr. McLaughlin soon learned was pressing against a nerve in his arm  that would improve their patients’ lives.

The trial, moreover, would cost $100 million and delay the possibility of F.D.A. approval by at least two years. To some doctors, it seemed a waste of time and resources that would be better used for trials testing what everyone most cared about: how to prolong the remissions.

There was reason to believe that combining PLX4032 with other drugs  some from competitors  would make it more effective. But researchers had to rely on Roche for permission until the drug was available for sale, and the company had not been forthcoming.

Dr. Chapman of Sloan-Kettering came up with a new tack: an unconventional bid to speed the drug’s approval, rooted in the observation that patients weeks or days from death could get out of bed and off oxygen when given PLX4032, sometimes for months. The doctors working with the drug referred to this as the Lazarus effect; it was unheard of with dacarbazine.