IDH1 and astrocytoma (excluding glioblastoma): IDH-mutant astrocytomas are now graded from 2 to 4 and separated from IDH-wildtype glioblastomas, thus obsoleting the term “glioblastoma, IDH-mutant.” The grading of astrocytoma may incorporate molecular markers alongside traditional pathological morphology; for example, the presence of cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) deletion indicates a poorer prognosis and categorizes these tumors as grade 4, even in the absence of microvascular proliferation or necrosis.7