NF1 and neoplasm: Additionally, the PTEN gene has been identified as a tumor suppressor that is recurrently mutated in GBM,[17] with deletion or mutation leading to dysregulation of the PI3K pathway.[18] Concomitant mutation of NF1 and PTEN is found almost exclusively within MES subtype tumors,[5] therefore small deletions were introduced to the NF1 and PTEN genes to recreate the genetic profile of the MES GBM subtype.