From University of Illinois at Urbana-Champaign
Sunlight, PCB exposure enhance skin cancer chances
CHAMPAIGN, Ill. -- Sunlight and PCB exposure can hit you where you least expect it. The combination enhances the development of non-melanoma skin cancer on parts of the body not directly exposed to the sun, according to a University of Illinois study.
Preliminary results of the research, which used the hairless mouse model of humans with non-malignant skin cancer, were presented today (March 21) in an exhibit at the 40th annual meeting of the Society of Toxicology in Nashville, Tenn. UI researchers also reported that PCB-exposed mice also ate more and grew fatter, regardless of exposure to light.
"The statistical power of our experiments leads us to believe that our results likely underestimate the strength of our conclusions," said Rhian B. Cope, a professor of veterinary biosciences in the UI College of Veterinary Medicine. "Because PCB-contaminated soil and sun exposure are both extremely common, we must look at this issue in humans."
In the study, funded by the American Cancer Society, researchers exposed a group of mice for 77 days to soil from a Southern Illinois landfill site contaminated with polychlorinated biphenyls and polychlorinated dibenzofurans, a PCB byproduct. Some of the mice were then exposed five days a week for 28 weeks to solar ultraviolet radiation.
Researchers found that the PCB-sunlight combination led to a rapid growth of non-melanoma tumors on the non-light-exposed undersides of the mice. The tumors were slow growing and did not turn into squamous cell carcinomas, "thus demonstrating their low malignant potential," the authors noted. PCB-exposed mice kept out of the light did not develop such tumors.
By day 281, other results surfaced. Mice exposed to sunlight but not the contaminated soil had developed twice the number of skin tumors in light-exposed areas than had PCB- and light-exposed mice. It was believed that the PCB-PCDF-contaminated soil, which caused chloracne (an acne-like eruption associated with dioxin exposure), served as a sunscreen, at least during early stages of exposure to UV light, Cope said.
"Our results were complex, but it was clear that tumor growth was dependant on whether or not an animal's skin was irradiated," Cope said. "The only time we saw tumors at any site was in the presence of UV irradiation. It was clear that UV light promotes the development of tumors at non-light-exposed sites that were probably initiated by exposure to PCBs and PCDFs."
In 1998, according to the American Academy of Dermatology, there were up to 1.2 million cases of non-melanona skin cancers in the United States, a number that may be underreported, Cope said. Soil used in the study came from the Sangamo Landfill on the Crab Orchard Wildlife Refuge, said collaborator Larry G. Hansen, a professor of veterinary biosciences. "It had a high PCB content, at least as high as some areas in Anniston, Ala."
Numerous lawsuits have resulted since the 1970s, when Monsanto ended 40 years of production of PCB, which was used to insulate electrical transformers, at its Anniston plant. "PCB contamination is a more widespread problem than most people realize," Hansen said, noting that millions of dollars are being spent on clean-up projects on the Hudson River in the northeast and in the Anniston area. "Several industrial areas of Europe also are highly contaminated," he added.
Hansen will present additional findings of the study at the Second PCB Workshop, May 7-11, in Brno, Czech Republic. He also will chair a session on human exposure and health effects, during which he will discuss human exposure at Anniston.
The UI study also will be detailed during the American Society of Photobiology annual meeting, July 13-17, in Quebec. Working with Cope and Hansen on the project are veterinary student Kanjana Imsilp and Carla K. Morrow, a research associate, both of the department of veterinary biosciences.