IDH1 and astrocytoma (excluding glioblastoma): Of the 25 primary IDH-mutant astrocytomas CNS WHO grade 2–4, 23 were subclassified as astrocytoma, IDH-mutant of lower-grade (calibrated scores 0.50–0.99) and the proportion of cases predicted as astrocytomas, IDH-mutant of high-grade, increased at recurrence (Fig. 1).