A compound that blocked the development of the distinctive markings of tadpoles in experiments could help to prevent the deadliest form of skin cancer, British scientists said on Thursday.

It may be able to stop the uncontrolled movement and growth of the pigment cells in tadpoles and humans that cause melanoma, they said.

Melanoma is an aggressive, difficult-to-treat cancer that kills most patients with advanced stages of the disease. Current therapies have only a limited impact or are highly toxic.

The World Health Organization estimates as many as 60,000 people each year die from too much ultraviolet light, mostly from malignant melanoma, the most aggressive form of skin cancer.

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"Once the cells migrate to other parts of the body and form secondary tumors, melanoma is difficult to treat by surgery or chemotherapy and often leads to death," said Grant Wheeler, a researcher at Britain's University of East Anglia, who led the study.

He and colleagues studied Xenopus laevis tadpoles, the young of South African clawed frogs. They first examined 2,000 compounds listed by the U.S. National Cancer Institute in search of one that might potentially block pigment cell movement.

The most promising was a so-called metalloproteinase inhibitor known as NSC 84093.

They dissolved the compound into water and let fertilized frog eggs develop in the solution. As the embryos turned into tadpoles, the movement of the pigment cells stopped and the tiny amphibians did not develop the usual distinctive markings.

The findings published in the Cell Press journal Chemistry and Biology suggest the drug could one day stop the mutant melanocytes that cause skin cancer from spreading in the body, but the next step is examining the compound's role in cell growth on other animals, Wheeler said.

"We hope to get a potential therapy for humans in the future, but this is still early days," he said.

"The next step is to test the compound in other species and, in the longer term, embark on the development of new drugs to fight skin cancer in humans,"