Made by Genentech, a US subsidiary of the Swiss pharmaceutical giant Roche, the Drug, Zelboraf, was approved by the US Food and Drug Administration in August 2011, making it the first new treatment for melanoma in 13 years.

The latest study, an intermediate phase II trial whose results are published in the New England Journal of Medicine, followed 132 patients at 13 medical sites in the US and Australia.

Study subjects survived an average of 15.9 months, when typical survival among people whose melanoma has spread to other organs is about nine months, it said.

"We knew this drug would make the melanomas shrink in a large proportion of patients and that it worked better than chemotherapy," said senior author Antoni Ribas, a professor of hematology and oncology and researcher at University of California Los Angeles's Jonsson Cancer Center.

"We did not know that patients taking Zelboraf were living longer until now."

The drug can be used to treat about half of all patients with metastatic melanoma, or about 4 000 patients in the US each year, the researchers said.

Zelboraf, a twice-a-day pill, works by blocking a protein that is involved with cell growth in patients with advanced melanoma whose tumours express a gene mutation called BRAF V600E.

About 53% of patients with that mutation see their tumours shrink by more than 30%, while an additional 30% of patients see tumours get smaller but not quite as much.

The drug failed to elicit a response in 14% of patients.

Another drawback is that patients appear to develop resistance to the treatment over time, but scientists are trying to find ways to stop that from happening, Ribas said.

Patients with advanced melanoma have few options for effective treatment, with less than 10% showing a response to other available therapies, the study authors said.

The National Cancer Institute says 68 130 new cases of melanoma were diagnosed in the US in 2010 and about 8 700 people died from the disease.

According to the World Health Organisation, skin cancer leads to 66 000 deaths annually worldwide, 80% of which involve melanomas.