AICDA and cancer: Although it has been proposed that C:G>A:T mutations are a less likely outcome of AID/APOBEC enzymatic action, we found a significant excess of these transversions in many cancers (Figure 4 and Supplementary Table S8), suggesting that a significant portion of C:G>A:T mutations may be caused by processes initiated by deamination by AID/APOBEC enzymes.