IDH1 and cholangiocarcinoma: Kipp and colleagues first identified IDH1/2 mutations in cholangiocarcinomas and a high frequency of IDH1/2 mutations in ICCs compared with a low frequency of IDH1/2 mutations in extrahepatic cholangiocarcinomas (28% vs. 7%, P = 0.030); they characterized the histological features of IDH1/2-mutated tumors as poor differentiation, clear cytoplasm, organoid arrangement of tumor cells, and relatively little desmoplasia5.