Similar observations were made in three additional cell lines, namely human hepatocellular carcinoma cells (HepG2), mouse embryonic stem cells (mESCs), and mouse B cell lymphoma cells (CH12), with cooccupancy of CTCF and RAD21 at a majority of sites (93.6 to 95.4%) observed in each case, and relatively low numbers of sites bound by CTCF but not RAD21 and vice versa (Fig. 1D). The gene discussed is RAD21; the disease is hepatocellular carcinoma.