IDH1 and cholangiocarcinoma: First, the TERT-mutated group, which correlates with the intermediate subtype; second, the TP53-mutated-only subgroup; third, the group without mutation; and fourth, the ARID1A-mutated, KRAS-mutated, and IDH1/2-mutated groups [35], the latter correlating with the cholangiocellular subtype now classified as cholangiocarcinoma [21].