Detection of 2-hydroxyglutarate in formalin-fixed paraffin-embedded glioma specimens by gas chromatography/mass spectrometry.

Mutations in the isocitrate dehydrogenase (IDH) 1 and 2 genes occur frequently in diffuse astrocytoma and oligodendroglioma. The consecutive amino acid substitutions in the mutant proteins result in a gain of the function to catalyze the reduction of alpha-ketoglutarate to 2-hydroxyglutarate (2HG). So far, all investigated IDH mutations share this gain of function. We here describe a method to detect 2HG levels in archival formalin-fixed paraffin-embedded tumor specimens by stable isotope dilution using gas chromatography followed by mass spectrometry (GC/MS). While 2HG levels are notably decreased during the routine embedding process, preserved amounts are still sufficient to indicate a mutation. Detection of 2HG in archival specimens could make routinely processed tissue accessible for research on 2HG accumulation and may allow studies on correlation with clinical data.