RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells, and may be an effective treatment for anaplastic oligodendroglioma. Combining combination chemotherapy with radiation therapy may kill more tumor cells.

PURPOSE: Randomized phase III trial to compare radiation therapy with and without combination chemotherapy in patients with resected anaplastic oligodendroglioma.

OBJECTIVES: I. Compare survival and time to first progression in patients with anaplastic oligodendroglioma treated with radiotherapy with or without adjuvant procarbazine, lomustine, and vincristine (PCV) following surgical resection. II. Investigate the effect of PCV on quality of life and neurologic function in these patients. III. Determine the toxicity of PCV in these patients. IV. Correlate chromosomal lesions (1p and/or 19q, 9p, p53 loss and mutation, amplification of chromosome 7, or loss of chromosome 10) with progression-free and overall survival in patients treated with these regimens.

OUTLINE: This is a randomized, multicenter study. Patients are stratified according to age, extent of resection, performance status, prior surgery, and participating center. Patients are randomized to one of two treatment arms. Arm I: Within 4-6 weeks after surgery, patients undergo radiotherapy over 7 weeks to the residual tumor volume. Arm II: Patients undergo radiotherapy as in arm I, then begin chemotherapy within 4 weeks after the completion of radiotherapy. Patients receive oral lomustine on day 1, oral procarbazine on days 8-21, and vincristine IV on days 8 and 29. Treatment repeats every 6 weeks in stable and responding patients for a total of 6 courses. Patients with disease recurrence may receive 6 additional courses of chemotherapy as above or another modality at the investigator's discretion. Patients are followed every 3 months for 1 year and then every 6 months for survival.

PROJECTED ACCRUAL: A total of 350 patients will be accrued for this study within 4 years.

DISEASE CHARACTERISTICS: Newly diagnosed oligodendroglioma or oligoastrocytoma (with at least 25% oligodendral elements) Low-grade oligodendroastrocytoma or oligodendroglioma that is recurrent after surgery without radiotherapy is allowed Prior partial or gross total resection of tumor (or biopsy only in case of no further surgical option) required At least 3 of the following histologic anaplastic features: High cellularity Endothelial abnormalities Nuclear abnormalities Necrosis Mitoses

PATIENT CHARACTERISTICS: Age: 16 to 69 Performance status: ECOG 0-2 Life expectancy: At least 3 months Hematopoietic: WBC at least 3,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.4 mg/dL Renal: Creatinine no greater than 1.3 mg/dL Creatinine clearance at least 60 mL/min Other: Not pregnant or nursing Fertile patients must use effective contraception No active or uncontrolled infection No other disease, including malignancy, that would preclude study No neurologic or psychiatric disturbance that would preclude study

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics No prior radiotherapy to the skull Surgery: See Disease Characteristics