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Inflammation, a frontline defense against infection or disease, can help nurture skin cancer, researchers have found.
IDO, an enzyme that works like a firefighter to keep inflammation under control, can be commandeered to protect early malignant cells, say Medical College of Georgia researchers studying an animal model of chronic inflammation and skin cancer. "Inflammation should really help prevent a tumor," says Dr. Andrew Mellor, director of the MCG Immunotherapy Center and Georgia Research Alliance Eminent Scholar in Molecular Immunogenetics.
In fact, there is strong evidence that inflammation triggers the immune response. "You want a good immune response; this is what protects you from pathogens," he says. "In this case, it's an unfortunate exploitation by malignant cells."
In a study with Drs. George C. Prendergast and Alexander J. Muller at the Lankenau Institute of Medical Research in Philadelphia, researchers gave mice a single dose of a carcinogen at the same time they began painting a tiny portion of skin with a poison ivy derivative twice weekly for 20 weeks. IDO quickly became part of the mix, creating a "suppressive" immune response that helped resulting precancerous cells grow into tumors, according to research published online in Proceedings of the National Academy of Sciences. When they used the same protocol in a mouse in which IDO had been genetically deleted, tumor development dropped off dramatically.
The scenario is analogous to chronic sun exposure and skin cancer, says Dr. Mellor, the study's corresponding author. Ultraviolet radiation in sunlight causes malignant skin cells to appear but sun exposure also causes skin inflammation, as evidenced by sunburn.