IDH1 and astrocytoma (excluding glioblastoma): GBM IDH wildtype is prevalent (~90% of all cases), mostly primary, and always regarded as Grade 4; whereas the GBM (or astrocytoma, according to WHO CNS5) IDH mutant is frequently characterized as Grade 2 or 3, and Grade 4 is a more common feature of the secondary one and so is considered as more prognostically optimistic [5].