APOB and neoplasm: Moreover, we found that all tumor samples bore aberrant apolipoprotein B mRNA-editing enzyme, catalytic polypeptide (APOBEC) cytidine deaminase activity with a higher frequency of mutations in chromatin regulation and DNA repair genes, such as lysine methyltransferase 2A (KMT2A), KMT2C, AT-rich interaction domain 1A (ARID1A), TP53, and ATRX chromatin remodeler (ATRX).