In previous CNS classifications, the glioblastoma multiforme is defined as Grade 4 astrocytoma and is divided into either isocitrate dehydrogenase (IDH) mutant or IDH wild; however, since the WHO CNS Classification 2021 update, glioblastoma multiforme is nominated as glioblastoma with IDH wild type, and the other similar histology with IDH mutant variant is called astrocytoma Grade 4 [2]. The gene discussed is IDH1; the disease is glioblastoma.