The most deadly form of skin cancer could be effectively treated using an arthritis drug, research has suggested.
Leflunomide, which is commonly used to treat rheumatoid arthritis, was found to significantly reduce tumour growth in mice with human-like melanoma.
When combined with an experimental melanoma drug called PLX4720 the effect was even more powerful, the researchers found.
Working together, the two compounds virtually halted cancer growth.
The discovery, reported in the journal Nature, was made after scientists screened thousands of compounds in search of promising drug candidates.
The breakthrough could lead to the development of a new melanoma treatment within the next five years.
Dr Grant Wheeler, from the University of East Anglia's School of Biological Sciences, who co-led the joint British-US research, said: "This is a really exciting discovery - making use of an existing drug specifically to target melanoma.
"Deaths from melanoma skin cancer are increasing and there is a desperate need for new, more effective treatments. We are very optimistic that this research will lead to novel treatments for melanoma tumours which, working alongside other therapies, will help to stop them progressing."
The stage is now set for clinical trials to investigate the effect of leflunomide on melanoma patients.
Because the drug is already licensed to treat a human disease and known to be safe, the trials process should be faster than usual. The scientists say a new treatment for melanoma based on leflunomide could be available within five years.