These results have been confirmed using topical administration of DMBA/TPA.(62) However, although only papillomas were observed in the Vdr null mice, Rxrα null mice developed both basal cell carcinomas (BCC) and squamous cell carcinomas (SCC).(62) Subsequently, Ellison and colleagues(59) and our own group(63)demonstrated that Vdr null mice were also more susceptible to tumor formation after UVB, and many of the tumors were SCC and BCC, but Cyp27b1 KO mice were not. This evidence concerns the gene RXRA and skin basal cell carcinoma.