Mutations in isocitrate dehydrogenase (IDH)-1 or -2 (which we commonly refer to as IDH) are found in gliomas (60–80% [1, 2], acute myeloid leukemia (~20%) [3], cholangiocarcinomas (7–28%) [4–6] and in benign and malignant central cartilaginous tumours [7–9]. Here, IDH1 is linked to cholangiocarcinoma.