DISEASE CHARACTERISTICS: Histologically proven oligodendroglioma or oligoastrocytoma with at least 25% oligodendroglial elements Recurrent or progressive disease following radiotherapy At least 3 months since prior radiotherapy Measurable disease by MRI or CT scan Lesion must have a diameter of at least 1 cm No progressive neurological deficits from the present recurrence No new neurological deficits interfering with daily activities No tumor causing midline shift or brain stem compression due to which a rapid deterioration is to be expected in case of no response No signs of increased intracranial pressure No extracranial disease

PATIENT CHARACTERISTICS: Age: 18 to 70 Performance status: WHO 0-2 Life expectancy: At least 3 months Hematopoietic: Neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.25 times upper limit of normal (ULN) AST/ALT no greater than 2 times ULN Alkaline phosphatase no greater than 2 times ULN Renal: Creatinine clearance at least 60 mL/min Creatinine no greater than 1.25 times ULN Neurologic: See Disease Characteristics Other: Not pregnant or nursing Fertile patients must use effective contraception No other malignant or nonmalignant diseases interfering with follow-up No psychological, familial, sociological, or geographical condition potentially hampering compliance with the study and follow-up

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics Surgery: Not specified Other: No other concurrent investigational drugs No other concurrent antitumor agents