While TP53 mutations are common in UV-driven MCCs, they are rare in viral-driven MCC (10, 43, 45, 102) conceivably because sTAg upregulates MDM2 and the MDM4 activator CK1α to repress p53, thus abrogating the need for mutational inactivation (149). This evidence concerns the gene MDM2 and Merkel cell skin cancer.