DISEASE CHARACTERISTICS: Histologically confirmed anaplastic astrocytoma or anaplastic oligoastrocytoma in first relapse Recurrence or progression at least 6 months from initial diagnosis Must have received maximally feasible surgical resection and fractionated external beam radiotherapy Must have received no more than 1 prior systemic cytotoxic chemotherapy regimen for initial disease Bidimensionally measurable disease by MRI scan (stable dose of corticosteroids for at least 7 days prior to scan)