IDH1 and astrocytoma (excluding glioblastoma): In 2021, the World Health Organization (WHO) amended its definition of GBM to follow genetic guidelines in addition to histological guidelines, requiring a diagnosis of GBM to lack isocitrate-dehydrogenase 1 and 2 mutations (IDH-wildtype); IDH-mutant grade IV gliomas are now termed IDH-mutant astrocytomas [2].