These data, alongside in vitro research showing mutant IDH produces the onco-metabolite D-2-hydroxyglutarate (2-HG) that can promote tumorigenic phenotypes (25, 26), suggests that this may be a significant factor in the secondary progression of lower grade gliomas (e.g. astrocytomas and oligodendrogliomas) to GBM rather than the generation of primary tumors. This evidence concerns the gene IDH1 and glioma.