Multiple lines of evidence, including the sequence context of SBS2/SBS13 mutations in human cancers35, engineered expression of APOBEC enzymes in model systems35,36 and APOBEC gene knockouts37 in human cancer cell lines, indicate that among the family of 11 APOBEC enzymes, APOBEC3A and, to a lesser extent, APOBEC3B are responsible for generating SBS2/SBS13. Here, APOBEC3B is linked to cancer.