IDH1 and intrahepatic cholangiocarcinoma: Mutations in IDH1/2 are found in approximately 13%–36% of intrahepatic cholangiocarcinoma cases and are less common in extrahepatic cholangiocarcinoma, constituting less than 1% of instances (Valle et al., 2017; Boscoe et al., 2019; Abou-Alfa et al., 2020a).