Accumulation of the 2-HG enantiomers L2-HG or D2-HG can occur under the following conditions: i) as pathologic metabolites in hypoxic cancer cells produced by lactate dehydrogenase (LDH) or malate dehydrogenase (MDH), respectively, [99–101]; or ii) as “oncometabolites” as a consequence of gain-of-function mutations in the genes coding for isocitrate dehydrogenase 1 or 2 (IDH1 or IDH2) [102, 103]. This evidence concerns the gene IDH1 and cancer.