For the melanoma patients who signed on to try a drug known as PLX4032, the clinical trial was a last resort. Their bodies were riddled with tumors, leaving them almost certainly just months to live.

But a few weeks after taking their first dose, nearly all of them began to recover.

Lee Reyes, 30, of Fresno, Calif., who had begun using a feeding tube because of a growth pressing against his throat, bit into a cinnamon roll.

Nothing, he told his mother, had ever tasted as good.

Rita Quigley, who had been grateful just to find herself breathing each morning since learning she had the virulent skin cancer, went shopping for new clothes with her daughters at a mall in Huntsville, Ala.

Randy Williams, 46, who drove 600 miles from his home in Jonesboro, Ark., to the M.D. Anderson Cancer Center in Houston to get the experimental drug, rolled out of bed. “Something’s working,” he thought, “because nothing’s hurting.”