PTEN and glioblastoma: In recurrent glioblastoma, there is the preservation of clonal mutations such as telomerase reverse transcriptase (TERT) [22] and phosphatase and tensin homolog (PTEN) [23], with a relative loss of epidermal growth factor receptor (EGFR) mutations and amplification [21,24,25] and overexpression of platelet-derived growth factor receptor (PDGF-R).