Secondary GBM and its precursors harbor isocitrate dehydrogenase [NADP(+)] 1 (IDH1) and 2 (IDH2) mutations (collectively IDHmut), in addition to either TP53 mutations in low-grade astrocytoma (LGA) and high-grade astrocytoma (HGA), or co-deletion of chromosome 1p/19q in oligodendroglioma (ODG) (11, 22). Here, IDH2 is linked to astrocytoma (excluding glioblastoma).