DISEASE CHARACTERISTICS: Histologically confirmed supratentorial malignant primary glioma Glioblastoma multiforme (closed to accrual as of 05/31/2001) Gliosarcoma (closed to accrual as of 05/31/2001) Anaplastic astrocytoma Anaplastic oligodendroglioma Mixed malignant gliomas Original histological diagnosis of low-grade glioma allowed if a subsequent histological diagnosis of malignant glioma is confirmed Prior treatment for no more than 2 prior relapses allowed Disease progression documented by at least 2 pre-study brain scans Recent prior tumor resection of recurrent or progressive tumor allowed if recovered from the effects of prior surgery