IDH2 and cholangiocarcinoma: Somatic mutations in the isocitrate dehydrogenase 1 and 2 genes affecting point mutations in the active-site arginine residues of isocitrate dehydrogenase (IDH), such as IDH1/R132, IDH2/R140, and IDH2/R172, occur frequently in many cancers, including chondrosarcoma, cholangiocarcinomas, and acute myelogenous leukemia [14–22].