Viral sequence analyses in MCC consistently show that tumor-derived LT antigens contain mutations that prematurely truncate the C-terminal helicase domain, while preserving the N-terminal tumor suppressor targeting domains for Rb-binding and DnaJ chaperone-binding functions (Grundhoff and Fischer, 2015; Wendzicki et al., 2015; DeCaprio, 2017). Here, RB1 is linked to Merkel cell skin cancer.