PTEN and glioblastoma: Although c-Myc gene amplification or rearrangement is uncommon in GBM [19], concomitant inactivation of p53 and PTEN was found to be a common event in a subset of primary GBMs, and simultaneous inactivation of p53 and PTEN lead to increased c-Myc expression and an undifferentiated phenotype in murine neural stem cells [20].