IDH1 and glioblastoma: In the 2021 fifth edition of the World Health Organization (WHO) classification (CNS5), diffuse gliomas were reorganized with molecular criteria taking center stage; under this schema, glioblastoma is restricted to IDH-wildtype (IDH-WT) tumors and can be diagnosed by histologic features or, in the appropriate setting, by the presence of a telomerase reverse-transcriptase promoter (TERT-p) mutation, EGFR amplification, or the combined whole-chromosome copy-number change of +7/−10, even in the absence of classic histology [1,2,3].