IDH-mutant gliomas diagnosed as primary GBMs are likely progressed astrocytomas that evaded earlier diagnosis (Ohgaki and Kleihues, 2013), as they frequently contain astrocytoma signature mutations—IDH1 (85%), TP53 (81%) and ATRX (71%; Liu et al., 2012). Here, IDH2 is linked to astrocytoma (excluding glioblastoma).