CDKN2A and glioblastoma: On the basis of the 2021 updated classification, additional molecular biomarkers have become essential to categorize adult gliomas including: H3.3 Histone A (H3.3A) mutations for diffuse midline gliomas, telomerase reverse transcriptase (TERT) promoter mutations, epidermal growth factor receptor (EGFR) gene amplification and chromosome 7 gain combined with loss of chromosome 10 for glioblastoma (GBM), and homozygous deletions of both cyclin dependent kinase inhibitor 2A (CDKN2A) and cyclin dependent kinase inhibitor 2B (CDKN2B) loci for IDH-mutant astrocytoma (7).