Oligodendroglioma (WHO grade II) is a well-differentiated tumor, composed predominantly of cells morphologically resembling oligodendroglia, which grows diffusely in the cortex and white matter. This tumor accounts for approximately 50% of oligodendroglial tumors and between 5% and 18% of all gliomas.

 Most oligodendrogliomas occur in adults, with a peak incidence in the fifth and sixth decades of life. Compared to patients with astrocytoma, patients with oligodendroglioma respond better to radiation therapy and chemotherapy. Temozolomide appears to have activity in low-grade oligodendrogliomas and oligoastrocytomas combined with a 1p allelic loss. Clinical improvement was noted in 51% of patients, and the radiologic response rate was 31%.

Anaplastic oligodendroglioma (WHO grade III) is an oligodendroglial tumor with focal or diffuse histologic features of malignancy and a less favorable prognosis than grade II oligodendroglioma.

 Approximately 50% of oligodendroglial tumors are anaplastic oligodendrogliomas. These types of tumors manifest mainly in adults and occur primarily in the frontal lobe and secondarily in the temporal lobe. In a study of 39 patients, chemotherapy was effective in tumors with a chromosomal abnormality (i.e., an allelic loss at 1p and 19q, which is present in 65% of tumors) with a response rate to combination therapy with procarbazine, lomustine, and vincristine (PCV) approaching 100%. The 5-year survival rate in this group was 95%. See review articles here, here, here, here, here, here, here, here