IDH1 and intrahepatic cholangiocarcinoma: IHC: intrahepatic cholangiocarcinoma, ECC: extrahepatic cholangiocarcinoma, IDH: isocitrate dehydrogenase, FGFR: fibroblast growth factor receptor, KRAS: Kirsten rat sarcoma virus, TP53: tumor suppressor 53, MDM2: mouse double minute 2, CDKN2A/B: cyclin-dependent kinase N2A/B.