IDH1 and cholangiocarcinoma: First, the what: every patient with advanced CCA should undergo testing for the full set of clinically actionable alterations, most prominently FGFR2 fusions/rearrangements, IDH1-mutations, ERBB2/HER2 amplification/overexpression, MSI-high/dMMR, NTRK-fusions, BRAF V600E, KRAS p.G12C, and selected emerging but still investigational targets (e.g., RET-fusions, NRG1-fusions, MDM2-amplification, BRCA1/2-alterations).