In CCA, the most common mutations of IDH1 are R132C (more frequent), R132G and R132L, which are distinct from the R132H mutation found in gliomas [155,162,163]; nevertheless, these activating alterations have been shown to increase the serum level of 2-HG in cholangiocarcinoma [160]. The gene discussed is IDH1; the disease is cholangiocarcinoma.