CDKN2A and glioblastoma: In primary glioblastomas, there is often loss of the INK4A/ARF (cyclin-dependent kinase inhibitor 2A/B—CDKN2A) gene locus, mutations in the phosphatase and tensin homolog deleted on the chromosome 10 (PTEN) gene, and amplification or loss of the epidermal growth factor receptor (EGFR) gene (Table 1) [11].