IDH1 and oligodendroglioma: Analysis of over 1000 cases identified five principal groups based on IDH mutation, 1p/19q codeletion, and TERT mutation status—most GBMs and GBM‐like LGGs had only TERT mutation; “triple‐positive” LGGs demonstrated favorable prognosis, oligodendroglioma histology; LGGs with only IDH mutation were molecular astrocytomas with intermediate prognosis; and worst prognosis LGGs had only TERT mutation suggestive of Grade IV behavior.