The better prognosis of patients with GBM-O compared to those with classic glioblastoma in this series may then at least partly be explained by the fact that these GBM-Os were more often secondary glioblastomas with IDH mutation occurring in younger patients with dedifferentiated tumors [56], a clinical and molecular subtype already known for a better prognosis. This evidence concerns the gene IDH1 and glioblastoma.