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Visible, UV-A light tied to skin cancer.

Even with frequent applications of sunscreen, the millions of people now enjoying their summer outdoors may be putting themselves at increased risk of melanoma, the most serious skin cancer.

Some visible light, as well as a wide range of ultraviolet (UV) light, may fuel a series of changes in skin cells, leading to melanoma, says Richard B. Setlow, a biophysicist at Brookhaven National Laboratory in Upton, N.Y.

He and his collegues use specially bred fish to study the effects of different types of light on cells that contain melanin, the skin pigment that colors moles brown. These studies have provided concrete evidence that not only UV-B -- the rays with wavelengths between 280 and 320 nanometers that cause sunburn -- but also light with longer wavelengths can induce cancer, says Setlow.

The fish are a cross between a swordtail and a hybrid of a swordtail and the platyfish, two popular tropical aquarium pets. When young, these heavily pigmented fish fit easily into the thimble-size glass tube of a spectrometer, which provides light of single wavelengths, and develop tumors after just one exposure to this light, Setlow explains. The pigment cells of the platyfish, like those of people, contain tumor-suppressing genes. Because the swordtail lacks such genes, some descendants of the cross possess just one tumor-suppressing gene and consequently less cancer protection.

Scientists have linked melanoma to damaged DNA because people who inherit a defect in their ability to repair DNA are more than 1,000 times more susceptible than others to this cancer. Many researchers had assumed that because DNA absorbs only UV-B energy, UV-B light caused the damage, says Setlow. Some suspected UV-A but lacked hard evidence of its role, he adds.

Then the Brookhaven group noticed that exposure to a wavelength of 365 nanometers -- the UV-A used in black lights -- resulted in tumors in 38 of the 85 fish tested. Furthermore, 30 of 124 fish not subjected to specific wavelengths but housed in a glass greenhouse as controls also developed melanoma, possibly due to sunlight, says Setlow.

Of 61 fish treated with violet light (405 nanometers), 18 developed melanoma. But only one of 20 control fish kept in subdued yellow light got cancer, they report in the July 15 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.

Setlow suggests that melanin absorbs light, which sets off a chemical reaction, producing compounds that then damage DNA. He urges that people protect themselves from all sunlight, something that sunscreens do not do.
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Title Annotation:study links visible and ultraviolet light to melanoma
Author:Pennisi, Elizabeth
Publication:Science News
Article Type:Brief Article
Date:Jul 24, 1993
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