These tumors frequently show oligodendroglial or ependymoma-like morphology with a delicate ‘chicken-wire’ vasculature and perivascular pseudorosettes, focal calcifications, occasionally microcystic/myxoid changes and malignancy features such as necrosis, frequent mitoses and microvascular proliferations, as well as frequent Olig2 expression. This evidence concerns the gene OLIG2 and ependymoma.