There is conflicting evidence regarding the prognostic role of IDH1 mutations for CCA [27, 28, 29, 30] and of its predictive impact in terms of response to standard chemotherapy; preclinical evidence indicated that mutant IDH1/2‐induced increase of 2HG leads to changes in DNA repair pathways [31, 32, 33, 34] and to homologous recombination deficiency (HRD). The gene discussed is IDH1; the disease is hypoparathyroidism-retardation-dysmorphism syndrome.