According to that, the 2021 Fifth Edition World Health Organization Classification of central nervous system (CNS) tumors has classified glioblastoma into two groups: IDH–wild-type glioblastoma (hereinafter referred to as GBM for simplicity) (95%) and IDH–mutant astrocytoma (5%) [2]. Here, IDH2 is linked to astrocytoma (excluding glioblastoma).