IDH1 and oligodendroglioma: Thus, astrocytomas and oligodendrogliomas will be diagnosed based on molecular characterization of the IDH and 1p/19q statuses; diffuse astrocytomas are defined by the presence of IDH1/IDH2 mutations without 1p/19q codeletion, whereas the diagnosis of oligodendrogliomas requires the presence of both IDH mutation and 1p/19q codeletion.