Misclassified IDH-mutant astrocytomas had increased copy number burden, especially on chromosome 10, were disproportionately WHO grade 4 (p < 0.0001, Fisher’s Exact), and followed a clinical course significantly worse than correctly classified IDH-mutant astrocytomas (OS = 2.8 vs 7.3 years, HR = 1.97, p < 0.001, log-rank) (Additional file 2: Fig. 4A, B, C). Here, IDH1 is linked to astrocytoma (excluding glioblastoma).