This news item from the Cornell Chronicle is about: Cornell researchers have discovered that when melanocyte stem cells accumulate a sufficient number of genetic mutations, they can become the cells where these cancers originate. Under normal conditions, ultraviolet (UV) radiation from the sun activates melanocytes to release melanin, a pigment that protects the skin from the sun’s rays. But if melanocyte stem cells have surpassed a threshold of genetic mutations, a tumor can start to grow when those skin stem cells are activated by sun exposure. “If you had mutations that were sufficient for melanoma, everything would be fine until you went out and got a sunburn,” said Andrew White, assistant professor of biomedical sciences at Cornell’s College of Veterinary Medicine, and senior author of a study published Oct. 12 in the journal Cell Stem Cell. Hyeongsun Moon, a postdoctoral researcher in White’s lab, is the paper’s lead author. “The stimuli that would normally just give you a tanning response could in fact start a melanoma instead,” White said.