A small clinical trial could provide a rare glimmer of hope for those with one of the deadliest forms of cancer.

Each year, 160,000 people are diagnosed with melanoma. When melanoma becomes metastatic, meaning that it spreads to other parts of the body, the median survival for the patient is less than a year. It has been one of the most difficult cancers to treat. Want to watch your favorite new cancer drug fail? Try it in patients with metastatic melanoma.

But a paper published today by the New England Journal of Medicine reports that one drug, code named PLX4032, has beaten the odds.

PLX4032 inhibits a mutated form of a protein called B-RAF. This particular mutation is found in roughly half of all melanomas, and 8% of all solid tumours. The mutation switches on B-RAF, which then accelerates tumour growth.

The clinical trial consisted of two segments. The first was a dose-escalation study, designed to find the best dose at which to treat patients. There were 55 patients in this cohort, 16 of whom had melanoma that carried the B-RAF mutation. Ten of the patients had a partial response, meaning that their tumours shrank by 30% or more, and one had a complete response, meaning that there was no trace of the tumours after treatment. A confirmatory study of 32 patients, all with B-RAF mutations, found that the drug yielded a partial response in 24 patients and a total response in two others.

In January, Plexxikon, the Berkeley, California company that developed the drug, announced that its partner Roche was embarking on a larger trial in 700 patients.

It was not always thus for PLX4032: in February, the New York Times published a moving series chronicling lead author Keith Flaherty’s struggle to find the right dose and formulation, and his initial disappointment when early results suggested that the drug performed poorly.

Unfortunately tumours do eventually become resistant the drug, as is the case with other genetically-targeted cancer therapies. The authors report that the duration of the response ranged from 2 to over 18 months, and at this point they don’t know how tumours eventually find a way around the drug. Many say that such targeted drugs need to be used in combination therapies, much in the same way that HIV patients take a combination of different anti-retroviral drugs to fend off resistance. But for now, in a disease where patients had little recourse, “the prospects for patients with metastatic melanoma have never been brighter,” writes Keiran Smalley and Vernon Sondak of the Moffit Cancer Center and Research Institute in Tampa, Florida in a related editorial.