Q: Why is the drug promising?

A: The drug, PLX4032, shrank tumors in 26 of 32 melanoma patients who had a key mutation in their tumors, according to a study in today's New England Journal of Medicine.

That's "remarkable," because patients in small, early trials such as this often get no benefit at all. Typically, experimental drugs shrink tumors in only 5% to 10% of patients, says Keiran Smalley of the Moffitt Cancer Center and Research Institute in Tampa, who wasn't involved in the study.

Some patients began showing improvement within only a few days, says Lynn Schuchter of the University of Pennsylvania, who also worked on the study.

Q: Were those patients cured?

A: In two patients, tumors disappeared, and some patients' disease remains in check. It's too early to know whether patients will stay in remission, however. The median remission was more than seven months, the study says.

But even shrinking tumors is relatively rare in advanced melanoma that has spread to other organs. The two approved drugs for melanoma — a chemotherapy called dacarbazine and an immune therapy called interleukin-2 — shrink tumors for only about 10% to 20% of patients, the study says.

Q: Does the drug help all patients?

A: No, it helps only the roughly 50% of patients whose tumors have the mutations in a gene called BRAF, the study says. Patients who don't have the mutation get no benefit.

If the drug is approved, doctors probably will begin testing all patients with advanced melanoma for the mutations. A test such as this probably would cost a few hundred dollars, says the study's lead author, Keith Flaherty of Massachusetts General Hospital in Boston.

Q: How is the drug different from other treatments?

A: Unlike conventional chemo, which kills all fast-growing cells, the new drug — also known as RG7204 — is considered a "targeted therapy" because it aims to block a specific mutation found only in certain melanoma cells.

Q: What about side effects?

A: Because PLX4032 leaves most healthy cells alone, it causes far fewer side effects than chemo, Flaherty says. High-dose IL-2, for example, can cause life-threatening side effects and is given only in the hospital, so patients can be closely monitored. Patients can take PLX4032, a pill, at home.

But even relatively mild side effects can become bothersome over time, says Vernon Sondak of the Moffitt Cancer Center and Research Institute in Tampa, who wasn't involved in the study.

If PLX4032 helps keep patients alive a long time — either by itself or when combined with other experimental drugs — patients may be more troubled by fatigue, rash and joint pain, Sondak says.

Q: Who financed the study?

A: The study was paid for by the drug's co-developers, Plexxikon and Roche Pharmaceuticals.

Q: What will it cost?

A: The companies haven't announced a price, because the drug is still in early trials. Flaherty notes, however, that many new cancer therapies cost $5,000 to $7,000 a month.

Q: Is it possible to get the new drug?

A: Yes. Doctors are still enrolling patients with advanced melanoma in a large trial of 680 patients who haven't gotten other treatment. Additional studies are expected to be launched next year, Flaherty says. More information about PLX4032 is available by calling 888-662-6728.

Other experimental drugs for melanoma — including ones very similar to PLX4032 — also are being developed. More information can be found at clinicaltrials.gov

Q: When might the drug be approved?

A: If additional studies are positive, Roche Pharmaceuticals plans to apply for FDA approval in 2011, spokeswoman Amy Berry says. In June, PLX4032 was given "fast-track" status by the Food and Drug Administration — a process that helps speed up development of drugs that fill unmet needs.