Revised: February 2004

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. Grading schemes for oligodendrogliomas are imperfect and do not correlate with prognosis as well as grading schemes for astrocytomas. Presently, oligodendrogliomas can be divided into those with low grade histology (i.e. lacking histologic features of aggressiveness) or anaplastic histology (i.e. showing mitoses, pleomorphism, endothelial proliferation and/or necrosis). In one study, the presence of contrast enhancement on imaging and endothelial proliferation were the best predictors of aggressive clinical behavior (1,2). Recent molecular studies have revealed a subtype of oligodendroglioma with a more favorable prognosis, regardless of histologic grade.  These favorable tumors show loss of heterozygosity at chromosome arms 1p and 19q [9].  In addition to a favorable prognosis, tumors with1p/19q deletions show marked chemosensitivity (>90%) and prolonged responses to radiotherapy

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 uncertain at this time. Although evidence exists that low grade oligodendrogliomas respond to chemotherapy (6), the impact on survival as compared to radiotherapy is unknown. Interest currently exists in treating patients with large diffusely infiltrating low grade oligodendrogliomas with up-front chemotherapy (primarily in hopes of reducing late radiation neurotoxicity). Molecular genetics is likely to play a key role in this decision-making process.  Oligodendrogliomas with 1p/19q deletions have a better prognosis and response to chemotherapy.  This group may do better with upfront chemotherapy and deferral of radiotherapy but this approach still requires confirmation.  Clinical trials are currently being established to address this issue.

Anaplastic oligodendrogliomas and mixed oligoastrocytomas should be treated with adjuvant therapy after resection or biopsy. Radiation therapy is the mainstay of adjuvant treatment and has shown increased survival in retrospective studies (3). Because as many as 70% of these tumours respond to chemotherapy in phase II trials (7) and adjuvant chemotherapy has been shown to be beneficial in anaplastic astrocytomas (8), combined modality therapy with radiation and PCV (procarbazine, lomustine and vincristine) chemotherapy should be discussed with these patients. A multi-centre phase III trial (NCIC/RTOG) has been completed to examine the survival benefit of up-front adjuvant PCV plus radiotherapy versus radiotherapy alone for anaplastic oligodendroglioma. This study is awaiting analysis and the results will likely influence further treatment.  Molecular genetics again are likely to be crucial in identifying patients most likely to benefit from additional chemotherapy.  Whether anaplastic oligodendrogliomas with 1p deletions can be managed with PCV chemotherapy alone is uncertain.  Trials by the RTOG will be addressing this question in the near future.  In the meantime, the decision to defer radiotherapy after successful chemotherapy should be made after discussion with both the patient and treating physicians.

References:

1. Daumas-Duport, C., et al., Oligodendrogliomas. Part I: Patterns of growth, histological diagnosis, clinical and imaging correlations: a study of 153 cases. Journal of Neuro-Oncology, 1997. 34(1): p. 37-59.
2. Daumas-Duport, C., et al., Oligodendrogliomas. Part II: A new grading system based on morphological and imaging criteria. Journal of Neuro-Oncology, 1997. 34(1): p. 61-78.
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. 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.
8. Levin, V.A., et al., Superiority of post-radiotherapy adjuvant chemotherapy with CCNU, procarbazine, and vincristine (PCV) over BCNU for anaplastic gliomas: NCOG 6G61 final report. International Journal of Radiation Oncology, Biology, Physics, 1990. 18(2): p. 321-4
9. Cairncross JG, et al.  Specific genetic predictors of chemotherapeutic response and survival in patients with anaplastic oligodendrogliomas.  J Nat Cancer Inst, 90:1473-79, 1998.