IDH2 and intrahepatic cholangiocarcinoma: Recently studies have found that the point mutation frequency of IDH2 is relative lower than that of IDH1, for example, in glioma (1.6–26.8%), intrahepatic cholangiocarcinoma (5.7–23.1%), and chondrosarcoma (10.7–19.4%), IDH2 R172 mutants include R172K (39%), R172S (29%), R172W (12%), R172G (10%), R172M (5%), and R172T (4%)11.