In contrast to AID, APOBEC3B exhibits a strong preference for deaminating C residues flanked by T. Although the function of APOBEC3B in normal conditions is unknown, APOBEC3B expression is correlated with frequencies of C:G>T:A transitions or C:G>G:C transversions in TpCpX motifs in several types of cancer, including breast cancer and lung cancer [36,48]. This evidence concerns the gene APOBEC3B and breast cancer.