Brain tumors with the histologicalfeatures of human GBM formed with 100% penetrance in both genotypes(Figure 1A–E).However, the rate of tumor formation differed significantly between these twogenotypes: mice with floxed Pten and p53 (Ptenf/f; p53f/f)had a median survival of 27 days post injection (dpi) compared to 85 dpi formice with floxed Pten (Ptenf/f). This evidence concerns the gene PTEN and glioblastoma.