In case of the presence of CDKN2A and CDKN2B homozygous deletion (CDKN2A/B-HD), the tumor is graded as “astrocytoma, IDH-mutant, grade 4,” even in the absence of histological features such as necrosis or microvascular proliferation [2]. This evidence concerns the gene IDH1 and astrocytoma (excluding glioblastoma).