While APE2 had a significant (α = 0.05) positive correlation with PCNA, APE1, XRCC1, PARP1, Chk1, and Chk2 across all 6 cancer types, groupings of DNA repair and DDR genes were found to be correlated with APE2 in different patterns in different cancer types (Figs. 4, and S14–S18). This evidence concerns the gene CHEK2 and cancer.