APEX1 and cancer: Another subgroup of PPIs presumably perturbed by cancers is characterized by negative or near-zero r-values in cancers and positive r-values of gene co-expression in conditionally normal tissues, for example, C1orf131/EIF3L, C19orf53/APEX1, C1orf198/PPP2R1A and C1orf198/ARHGEF1 (Table 3).