IDH2 and glioblastoma: Subsequently, the cIMPACT-NOW recommended upgrading those harboring homozygous deletion of CDKN2A (cyclin-dependent kinase inhibitor 2A) and CDKN2B (abbreviated as CDKN2A/B), either alone or in combination with microvascular proliferation or necrosis, to a newly described entity: IDH-mutant astrocytoma, WHO grade IV (to be distinguished from glioblastoma, WHO grade IV) [2].