Background: Oligodendrogliomas are rare central nervous system (CNS) tumors. Although surgery remains the primary treatment, the role of postoperative radiation treatment remains a matter of controversy. This study assesses whether postoperative radiation improves survival and local tumor control when compared with surgical treatment alone.
Methods: The medical records of 72 patients with the diagnosis of oligodendroglioma, registered at the Princess Margaret Hospital (PMH) between 1958 and 1984, were reviewed retrospectively. The data of 68 patients were evaluated, but 4 patients were excluded from the analysis because of inadequate follow-up. The median follow-up period at the time of analysis was 7.5 years. Tumors were classified as oligodendrogliomas, malignant oligodendrogliomas, or mixed oligoastrocytomas. Fifty-eight (85%) patients received postoperative irradiation at initial diagnosis, and 10 (15%) patients were treated with surgery alone. In most patients (76%), the radiation dose was 5000 cGy in 25 fractions given during a period of 5 weeks.
Results: Five- and 10-year overall survival was 66% and 30%, respectively. Forty-two (62.0%) patients experienced disease relapse during the follow-up period. The median time to relapse from initial diagnosis was 2.6 years. Most tumor recurrences were at the primary site. Two patients developed distant metastasis within the CNS axis. Histologic subtype was the only significant prognostic factor for survival. The patients with oligodendroglioma and malignant oligodendroglioma had 5-year survival rates of 73% and 32%, respectively (P = 0.033).
Conclusions: The authors drew three conclusions. (1) Most patients eventually died with this tumor from local recurrence without distant metastasis. Local tumor control remains the major problem. (2) Tumor histologic subtype is a significant prognostic factor. (3) No statistically significant benefit can be attributed to postoperative irradiation; however, the number of patients not receiving radiation therapy was small (10). Thus, the role of radiation therapy remains a matter of controversy.