Skin cancer risk varies substantially across the body, yet how this relates to the mutations
found in normal skin is unknown. Here we mapped mutant clones in skin from high-and low-
risk sites. The density of mutations varied by location. The prevalence of NOTCH1 and FAT1
mutations in forearm, trunk, and leg skin was similar to that in keratinocyte cancers. Most
mutations were caused by ultraviolet light, but mutational signature analysis suggested
differences in DNA-repair processes between sites. Eleven mutant genes were under …