Source and target gene groups that show a noticeable gap between their reachability probabilities in control versus leukemia cases include SPI1, POU2F2 as sources and TOPBP1, TFDP1, TFDP2, HDAC1, CDK8, REL, RELA and NFKB2 as targets. This evidence concerns the gene HDAC1 and leukemia.