ATRX nuclear loss is diagnostic for astrocytic- lineage tumors in an IDH-mutant gliomaTP53 mutations are commonly found in astrocytomasCDKN2A/B homozygous deletion is a marker of poor prognosis and upgrades Grade 2/3 IDH-mutant astrocytomas to Grade 4 astrocytomas. This evidence concerns the gene IDH1 and astrocytoma (excluding glioblastoma).