IDH1 and biliary tract cancer: In addition, a certain inconsistency on data provided furtherly complicates the matter, namely: a) data often refers to all biliary tract cancers and not specifically to iCCA; b) several trials do not distinguish between FGFR2 rearrangements and mutations or between IDH1 and IDH2; c) the definition of OS in not always unanimous, as the starting point can refer to the initial diagnosis in some trials and to the start of first-line chemotherapy in others.