A majority of oligoastrocytomas (63.8%) exhibited the IDH mutation in the absence of TERT promoter mutations, much like Grade II-III astrocytomas; however, a fraction (22.4%) of oligoastrocytomas presented with both TERT promoter and IDH1/2 mutations, similar to oligodendrogliomas (Fig. 1). Here, IDH1 is linked to oligodendroglioma.