APOBEC1 and cancer: We confirm that while the mutational footprints of APOBEC1, APOBEC3A, APOBEC3B, and APOBEC3G are prominent in many cancers, mutable motifs characteristic of the humoral immune response somatic hypermutation machine, AID, are the most widespread feature of the somatic mutation spectra attributed to APOBECs in cancer genomes.