Decoding the mystery of melanoma

Sixteen years ago, a scientific finding that exposure to ultraviolet A rays was the primary cause of melanoma in fish models surprised the scientific community.

It had been established that ultraviolet B rays — often absorbed in childhood — caused melanoma, but the new finding implied that researchers should also look at UVA. Sunscreens were reformulated to include protection against UVA. But many scientists were suspicious.

“It was controversial,” says David Mitchell, Ph.D., professor in the Department of Molecular Carcinogenesis at MD Anderson’s Science Park-Research Division in Smithville, Texas. “People questioned it.”

So Mitchell secured a National Cancer Institute grant to replicate the experiment in fish models. Last April, he published a paper from his larger study showing that fish exposed to UVA rays were no more likely than the control group to develop melanoma. Those exposed to UVB, however, were 240% more likely to develop melanoma.

Further study needed

This doesn’t mean that UVA plays no part in the growth of melanomas, Mitchell says. He’s working on a grant to study the effects of chronic UVA on the severity of melanoma and its progression after it has formed.

“The tanning industry worldwide uses UVA as a ‘safe’ alternative to full sunlight exposure,” he says. “We might help identify the causes of the dramatic increase in melanoma in the past 30 years and offer a scientific rationale for regulating the industry.”

Reported in May 2010 in the online early edition of the Proceedings of the National Academy of Sciences.