CDK4 and glioblastoma: Other common molecular genetic alterations associated with GBM include: phosphatase and tensin homolog (PTEN) mutations, epidermal growth factor receptor (EGFR) amplification, cyclin-dependent kinase 4 (CDK4) amplifications, and cyclin dependent kinase inhibitor 2A (CDKN2-A) homozygous deletion [9].