In accordance with the 2021 WHO classification criteria, the panelists reached a strong consensus that only IDH-wildtype grade 4 gliomas should be classified as glioblastoma and that IDH-wildtype astrocytic gliomas in adults should be considered glioblastoma if any of the following criteria are met: microvascular proliferation, necrosis, TERT promoter mutation, EGFR gene amplification, and +7/−10 chromosome copy number changes. This evidence concerns the gene IDH1 and glioblastoma.