Homozygous deletion of CDKN2A/B has been established as a marker of grade 4 IDH-mutant astrocytomas [18,19], and grade 4 glioblastoma is molecularly defined by TERTp mutation, EGFR amplification and chromosome 7+/10− [20]. This evidence concerns the gene IDH1 and astrocytoma (excluding glioblastoma).