Adult-type diffuse gliomas represent a group of primary brain tumors that comprises IDH-mutant astrocytoma, IDH-mutant and 1p/19q-codeleted oligodendroglioma, and IDH-wildtype glioblastoma according to the 2021 World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS) [45]. The gene discussed is IDH2; the disease is glioblastoma.