TP53 and glioblastoma: One of these studies showed MGMT-methylation in 43% of patients, EGFRvIII in 19%, and 1p19q codeletion in 2%; IDH1 mutations were observed in about 9% of glioblastomas (evolving from grade III astrocytomas) and were associated with MGMT-methylation and TP53 mutation and were mutually exclusive with EGFRvIII [158].