IRF4 and cholangiocarcinoma: Epigenetic studies in Ov-CCA have demonstrated abnormalities in DNA methylation with promoter hypermethylation observed in several genes, hMLH1 [15], Trop2 [16], RIZ1 [17], EBF1 [18], p14A2RF, p15INK4B, p16INK4A [19], PPP4C (DNA repair), RUNX3, IRF4, UCHL1, TP53I3 (apoptosis), CCND2, RASSF1 (cell proliferation), ALDH1A3, SLC29A1 (drug metabolism), HTATIP2 (angiogenesis) [20], OPCML, SFRP1, HIC1, PTEN, and DcR1 [8], OPCML [21].