In addition to deaminating viral genome, evidence also suggests that both APOBEC3A (A3A) and APOBEC3B (A3B) can catalyze C-to-T transitions in DNA, and these enzymes are strongly associated with cytosine-derived somatic mutations in cancer genomes, but only endogenous A3B is frequently upregulated in certain cancer types such as breast, ovary, head/neck, esophagus, among others8, 12, 13. Here, APOBEC3B is linked to cancer.