APOBEC3B (A3B) is the leading candidate for APOBEC mutagenesis in cancer, due to several independent lines of evidence including overexpression in tumors and cancer cell lines, nuclear localization, modulation by tumor-promoting viruses (including HPV and EBV), and associations with poor clinical outcomes (see, e.g., [11,16,22,25,26,27,28,29,30,31,32,33,34,35]). This evidence concerns the gene APOBEC3B and cancer.