Overexpression of the EGFR gene, loss of heterozygosity (LOH) on chromosome 10q that affects the phosphatase and tensin homolog (PTEN) gene, mutations in the TERT promoter, deletion of CDKN2A (p16), and, less frequently, amplification of mouse double minute 2 (MDM2) are the most common characteristics of primary GBM (6, 7, 37). The gene discussed is PTEN; the disease is glioblastoma.