Isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) are frequently mutated in low-grade glioma (LGG) and are found in 12% of GBM; they comprise a large proportion of secondary GBM and are rarely found concomitantly with EGFR mutations.27 In glioma pathogenesis, the IDH genes are strongly correlated with the CpG island methylator phenotype, which is markedly associated with improved survival clinically.74 Moreover, although IDH1 is strongly implicated in glioma pathogenesis, it has been unclear what role it plays in progression. Here, IDH2 is linked to glioma.