Genetically, amplification of the epidermal growth factor receptor (EGFR) locus is found in approximately 40% of primary glioblastomas but is rarely found in secondary glioblastomas; mutations of the tumor suppressor gene phosphatase and tensin homolog deleted on chromosome 10 (PTEN) are observed in 45% of primary glioblastomas and are seen more frequently in primary glioblastomas than in secondary glioblastomas [3]. The gene discussed is PTEN; the disease is glioblastoma.