Revised: June 2014

Initial treatment of oligodendroglioma is surgical. In feasible cases, gross total resection should be the goal. Pathology from surgery (biopsy or resection) should be reviewed. Oligodendrogliomas should be classified based on both histologic grade and molecular diagnostics.  Histologically, oligodendrogliomas are classified by the WHO grading system as low grade (Gr. II) or anaplastic (Gr. III) (1).  Low grade tumours show increased cellularity but no anaplastic features of elevated mitotic rate, vascular proliferation or necrosis.  Any of these features will lead to an anaplastic grading of the tumour.  The molecular classification of oligodendroglioma divides these tumours into those showing co-deletion of chromosomes 1p and 19q and those with retention of those chromosome arms.  Most tumours with 1p/19q co-deletion also show IDH1 mutation.  Low grade tumours and those with 1p/19q co-deletion are good prognostic markers (1).  In addition to a favorable prognosis, tumours with 1p/19q deletions show marked chemosensitivity (>90%) and prolonged responses to radiotherapy (2).

Low grade oligodendrogliomas typically have slow growth patterns and a better prognosis than most gliomas. Treatment of asymptomatic biopsy-proven low grade oligodendrogliomas is controversial (similar to low grade astrocytomas). Although adjuvant radiotherapy has been commonly advocated(3,4), there is evidence suggesting these lesions can be observed for clinical or radiographic progression without adversely affecting overall survival (with the potential benefit of delaying radiation related neurotoxicity)(5). In those with symptomatic residual disease after initial surgery, adjuvant radiotherapy is standard care and should be recommended. The role of adjuvant chemotherapy is currently under investigation. Although evidence exists that low grade oligodendrogliomas respond to chemotherapy (6,7), the impact on overall survival as compared to radiotherapy is unknown. Interest currently exists in treating patients with more indolent 1p/19q co-deleted with up-front chemotherapy (primarily in hopes of reducing late radiation neurotoxicity). Recent evidence from the RTOG 9802 trial indicates higher risk low grade gliomas (age >40, incomplete resection) have longer survival with combinations of chemotherapy and radiotherapy (8).Whether this data applies to all low grade gliomas or certain molecular and risk subsets requires further analysis.

Anaplastic oligodendrogliomas and mixed oligoastrocytomas should be treated with adjuvant therapy after resection or biopsy. Results of recent clinical trials have shown that chemotherapy with radiotherapy offers superior long term survival in anaplastic tumours with 1p/19q co-deletion (9). Radiation therapy alone remains the standard of care for non-deleted anaplastic tumours but interest remains in giving these patients GBM protocols of concurrent temozolomide and radiation.

References:

1. Louis DN, Ohgaki H, Wiestler OD, Cavenee WK (eds.). World Health Organization Histological Classification of Tumours of the Central Nervous System. Lyon: International Agency for Research on Cancer, 2007

2. Intergroup Radiation Therapy Oncology Group Trial 9402, Cairncross G, Berkey B, et al. Phase III trial of chemotherapy plus radiotherapy compared with radiotherapy alone for pure and mixed anaplastic oligodendroglioma: Intergroup Radiation Therapy Oncology Group Trial 9402. J Clin Oncol 2006; 24:2707.

3. Shaw, E.G., et al., Oligodendrogliomas: the Mayo Clinic experience. Journal of Neurosurgery, 1992. 76(3): p. 428-34.

4. Allison, R.R., et al., Radiation and chemotherapy improve outcome in oligodendroglioma [see comments]. International Journal of Radiation Oncology, Biology, Physics, 1997. 37(2): p. 399-403.

5. Karim, A.B.M.F., et al. Immediate postoperative radiotherapy in low grade glioma improves progression free survival, but not overall survival: preliminary results of an EORTC/MRC randomized phase III study. Proceedings of ASCO, 1998. 17:400.

6. Mason, W.P., G.S. Krol, and L.M. DeAngelis, Low-grade oligodendroglioma responds to chemotherapy. Neurology, 1996. 46(1): p. 203-7.

7. Hoang-Xuan K, Capelle L, Kujas M, et al.  Temozolomide as initial treatment for adults with low-grade oligodendrogliomas or oligoastrocytomas and correlations with 1p deletions. Journal of Clinical Oncology, 2004, 22:3133-38.

8. Buckner JC, Pugh SL, Shaw EG, et al.  Phase III study of radiation therapy with or without procarbazine, CCNU and vincristine (PCV) in low grade glioma: RTOG 9802 with Alliance, ECOG and SWOG.  J Clin Oncol 2014. 32:5s, abstr 2000.

9. Cairncross, G., et al., Chemotherapy for anaplastic oligodendroglioma. National Cancer Institute of Canada Clinical Trials Group. Journal of Clinical Oncology, 1994. 12(10): p. 2013-21.