IDH1 and astrocytoma (excluding glioblastoma): As of 2021, the WHO classification of tumors of the central nervous system has delineated glioblastoma through isocitrate dehydrogenase (IDH) expression, with IDH wild-type high-grade gliomas being glioblastomas and IDH-mutant high-grade gliomas being grade IV astrocytoma or oligodendrogliomas [1,5].