Expression of GLUD1, GLUD2, or both is tested in gliomas, leukemias, or suspected gliomas and leukemias. Up-regulation of expression is found in IDH1/IDH2 mutant cancers. Inhibition of GLUD1, GLUD2, or both can be used therapeutically to inhibit cancer growth. Assays for GLUD1, GLUD2, or both GLUD1 expression can measure RNA or protein or enzyme activity, for example.