It is now recognized that IDH-wild-type (WT) gliomas essentially represent primary glioblastomas (GBM), while IDH-mutant gliomas bearing (1p/19q codel) or not bearing (1p/19q non-codel) the co-deletion of 1p/19q encompass tumors previously classified as oligodendrogliomas and astrocytomas, respectively. This evidence concerns the gene IDH1 and glioblastoma.