Scientists have found a genetic mutation in melanoma skin cancer cells that increases the disease’s severity but which could also be a target for new drugs against the killer illness.

They studied cells from patients with early and advanced melanoma tumors and found extra copies of a gene called MITF.

About 10 percent of primary tumors and 21 percent of metastatic tumors - those that had spread beyond the original site - had up to 13 extra copies of the gene.

“By pinpointing the abnormally multiplied MITF oncogene, we may be able to develop better diagnostic and prognostic tools as well as provide a target for highly specific therapies for metastatic melanoma patients who have this overcopied gene,” said William Sellers of the Dana-Farber Cancer Institute in Boston, Massachusetts.

An oncogene is a gene that promotes cancer.

Melanoma is the deadliest type of skin cancer and is mainly caused by sun exposure. It accounts for roughly 10 percent of reported cases of skin cancer and can spread rapidly throughout the body, forming secondary tumors.

About 133,000 new cases of melanoma are diagnosed worldwide each year, according to the International Agency for Cancer Research in Lyon, France. Up to 80 percent of cases are in North America, Europe, Australia and New Zealand.

If the illness is caught early, before it has spread, the prognosis is good but metastatic melanoma does not respond well to treatment.

The scientists, who reported the findings in the science journal Nature, found the mutation by looking at regions of chromosomes where genetic deletions or additions are often linked to cancer.

After checking the outcomes of patients whose tumors were studied in the research, the scientists found that those with the MITF mutation had poorer 5-year survival rates.

The MITF mutation was also linked to other genetic changes such as mutations in a gene called BRAF and the silencing of a tumour suppressor gene known as p16, according to the scientists.

Additional copies of the MITF gene seems to promote the growth and survival of the tumour.

“We might be able to treat these metastatic melanomas by targeting the MITF gene or protein, alone or in combination with drugs that block BRAF,” Sellers said in a statement.

“We know that when MITF activity is reduced, melanoma cells become more vulnerable to chemotherapy drugs,” he added.