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Study Sheds New Light On Ultraviolet Rays and Melanoma Researchers at The University of Texas M. D. Anderson Cancer Center have found that the risk of developing melanoma, the most deadly form of skin cancer compared with nonmelanoma skin cancers, is only partially associated with exposure to ultraviolet B (UVB) radiation, the rays in sunlight that increase in summer and cause sunburn. The report in the December 21, 2005 issue of the Journal of the National Cancer Institute indicates that only nonmelanoma skin cancers (basal and squamous cell carcinoma) are strongly associated with exposure to UVB radiation. It is well known that in the general population, sun exposure increases a person’s risk of developing squamous cell carcinoma, but the risk of developing basal cell carcinoma increases to a certain point, given exposure to UVB radiation, and does not continue to increase with additional sun exposure. This does not mean, however, that sunbathing poses a minimal risk for developing melanoma. Researchers say that ultraviolet A (UVA) radiation, the rays in sunlight that reach the deeper layers of skin and are associated with signs of aging, can damage the DNA in melanocytes, the pigment-producing cells that give rise to melanoma. “Although we have refined the common wisdom that excess sun exposure is always associated with increased risk of skin cancer, the take-home message for the public is still the same—limit sun exposure and use a sunscreen that blocks both UVA and UVB rays,” said Qingyi Wei, M.D., Ph.D., a professor in the Department of Epidemiology at M. D. Anderson Cancer Center. Dr. Wei, the study’s lead investigator, said that there are several reasons why nonmelanoma skin cancers are so common—more than 1 million cases are diagnosed each year in the United States—and why they are so easy to treat. Squamous skin cells lie near the top of the skin’s layers, whereas basal skin cells lie near the base of the skin’s layers. In both cases, these cells actively reproduce. When their chromosomes are damaged by sunlight, the cells often die or form a nonmelanoma surface cancer that is easy to remove by surgery or treat in other ways, he said. The researchers reported a painstaking analysis of the ability of UVB radiation to damage a cell’s chromosomes. Dr. Wei’s group has shown in previous studies that melanoma patients often have a reduced capacity to repair the DNA damage that results from UVB exposure. In the current study, researchers found that UVB radiation damaged chromosomes more severely in patients with nonmelanoma basal and squamous cell carcinoma than in patients with melanoma. The frequency of UVB-induced chromosome breaks was higher in patients with nonmelanoma skin cancer than in the control group but was the same in melanoma patients and the control group. In fact, a higher frequency of chromosomal breaks was associated with a more than two-fold increased risk for both basal cell and squamous cell carcinoma, Dr. Wei said.For more information on this topic or for questions about M. D. Anderson’s treatments, programs, or services, call askMDAnderson at (877) MDA-6789. Other articles in OncoLog, March 2006 issue:
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