TP53 and skin cancer: In early skin cancer development, a single p53 allele is mutated or deleted as an early initiating oncogenic event.17 Patches/clones of mutant p53 keratinocytes (considered to be the precursor lesion to skin cancer) can be detected in sun-exposed areas of human skin and in UVB-treated mouse skin long before tumors form.17, 46, 47 Most of these clones have a single mutant allele of p53 (97% missense and 3% nonsense).17 Collectively, these studies indicate that mutation of a single p53 allele provides a pro-oncogenic function/advantage early in skin cancer development.