IDH1 and astrocytoma (excluding glioblastoma): The 2016 WHO CNS classification strongly discourages the diagnosis of oligoastrocytoma, claiming that nearly all tumors with histological features suggesting both an astrocytic and an oligodendroglial component can be classified as either astrocytoma or oligodendroglioma using genetic testing for IDH mutation and 1p19q loss [2,4].