From its classic role as a deoxycytidyl transferase [35], to maintaining trinucleotide repeat stability [36], to its roles in HR and NER [37,38], to its ability to unravel G4 quadruplexes [39], to regulating cell death responses in cancer cells [40,41], and its association with virus replication [42,43], REV1 has an expanded significance of its role in mutagenesis and genome instability. This evidence concerns the gene REV1 and cancer.