IDH2 and cholangiocarcinoma: Previous CCA gene expression analyses suggest the overexpression of S100A6, platelet-derived growth factor-alpha (PDGFA), neutral proliferation differentiation and control protein 1 (NPDC1), while the cytochrome P450, succinate dehydrogenase (SDHA), isocitrate dehydrogenase 2 (IDH2) and glutathione S-transferase-alpha4 (GSTA4) was downregulated (Wu et al., 2011).