IDH1 and glioblastoma: The p53 cell cycle and cell proliferation gatekeeping pathway, defined here by mutations in TP53 itself, as well as mutually exclusive mutations in MDM2, MDM4, RPL5, and PPM1D, was altered in approximately half of the IDH-wild-type and all IDH-mutant glioblastoma cases (Table 1 and Figure 1E).