Mutations in isocitrate dehydrogenases 1 or 2 (IDH1, IDH2) occur approximately in 75% of diffuse astrocytomas and oligodendroglial tumors[1-3], in 20% of acute myeloid leukemia (AML)[4,5], 50% of chondrosarcoma[6,7], 20% of intrahepatic cholangiocarcinoma[8] and in 20% of angioimmunoblastic T-cell lymphoma[9]. The gene discussed is IDH2; the disease is intrahepatic cholangiocarcinoma.