DISEASE CHARACTERISTICS: - Histologically confirmed diagnosis of 1 of the following: - Anaplastic oligodendroglioma - Anaplastic oligoastrocytoma - Anaplastic astrocytoma - Newly diagnosed disease - Prior surgery for a low grade tumor is allowed, provided histological confirmation of an anaplastic tumor is present at the time of progression - Absence of combined 1p/19q loss - Tumor material available for central 1p/19q assessment, central O6-methylguanine-DNA methyltransferase promoter methylation status assessment, and central pathology review - Patients must be on a stable or decreasing dose of steroids for at least two weeks prior to randomization PATIENT CHARACTERISTICS: - WHO performance status 0-2 - ANC ≥ 1.5 x 10^9 cells/L - Platelet count ≥ 100 x 10^9 cells/L - Bilirubin < 1.5 x upper limit of normal (ULN) - Alkaline phosphatase < 2.5 x ULN - AST and ALT < 2.5 x ULN - Serum creatinine < 1.5 x ULN - Not pregnant or nursing - Fertile patients must use effective contraception - No known HIV infection or chronic hepatitis B or hepatitis C infection - No other serious medical condition that would interfere with follow-up - No medical condition that could interfere with oral medication intake (e.g., frequent vomiting or partial bowel obstruction) - No prior or concurrent malignancies at other sites except for surgically cured carcinoma in situ of the cervix or nonmelanoma skin cancer - No psychological, familial, sociological, or geographical condition that would potentially hamper compliance with the study protocol and follow-up schedule PRIOR CONCURRENT THERAPY: - See Disease Characteristics - No prior chemotherapy, including carmustine-containing wafers (Gliadel®) - No prior radiotherapy to the brain - No concurrent growth factors unless vital for the patient - No other concurrent investigational treatment - No other concurrent anticancer agents