Due to the improved prognosis of tumours previously classified as IDH-mutant glioblastomas compared to IDH-wildtype glioblastomas, these have been reclassified as astrocytoma, IDH-mutant, CNS WHO grade 4 in the fifth edition of the WHO Classification of Tumours of the Central Nervous System (WHO CNS5, 2021). The gene discussed is IDH2; the disease is glioblastoma.