HOUSTON Early life exposure to ultraviolet A light does not cause melanoma in a fish model that previously made that connection, scientists from The University of Texas MD Anderson Cancer Center reported today in the online Early Edition of the Proceedings of the National Academy of Sciences.
UVA exposure is unlikely to have contributed to the rise in the incidence of melanoma over the past 30 years, the researchers conclude, because the fish model had been the only animal model to indicate a connection between exposure to UVA at a young age and later development of melanoma.
"Our data refute the only direct evidence that UVA causes melanoma, which is not to say that UVA is harmless," said the study's lead author David Mitchell, Ph.D., professor in M. D. Anderson's Department of Carcinogenesis located at its Science Park Research Division in Smithville, Texas. "UVA is just not as dangerous as we thought because it doesn't cause melanoma."
UVA is a carcinogen responsible for squamous cell carcinomas that also causes premature aging of the skin and suppresses the immune system. It's also possible, the authors note, that long-term chronic exposure to UVA can hasten the progression to malignancy of melanocytes in the skin that are already on the path to becoming melanoma.
Mitchell and colleagues tested the effects of UVA and ultraviolet B (UVB) light exposure in melanoma-prone fish hybrids that develop the disease spontaneously 15-20 percent of the time without exposure to UV light.
The scientists exposed a hybrid form of the genus Xiphophorus, more commonly known as platyfishes and swordtails, to either UVA or UVB daily between their fifth and 10th day of life. The fish were then scored for melanoma 14 months after exposure.
"We found that UVB exposure induced melanoma in 43 percent of the 194 treated fish, a much higher rate than the 18.5 percent incidence in the control group that received no U
|Contact: Scott Merville|
University of Texas M. D. Anderson Cancer Center