In mouse models of GBM, neither activated Ras nor Akt alone induce tumors; however, the combination of both activations can.40 Similarly, mouse models deficient in NF1 and p53 develop GBM-like tumors with all the characteristic features, including invasion, neovascularity, necrosis, and atypical astrocytes.49 This evidence concerns the gene TP53 and glioblastoma.