IDH1 and glioblastoma: 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.