PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior epoetin alfa, filgrastim (G-CSF), or sargramostim (GM-CSF) and recovered No concurrent immunotherapy Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy (2 weeks since vincristine; 6 weeks since nitrosoureas or mitomycin) and recovered No prior leflunomide (SU101) therapy No other concurrent chemotherapy Endocrine therapy: No concurrent hormonal therapy (except medroxyprogesterone acetate for appetite stimulation) Radiotherapy: See Disease Characteristics No more than 1 prior course of radiotherapy At least 8 weeks since prior radiotherapy and recovered No prior interstitial radiotherapy or implanted carmustine wafers Prior radiosensitizer(s) concurrent with radiotherapy or used as neoadjuvant therapy allowed No concurrent radiotherapy Surgery: See Disease Characteristics No more than 2 prior surgical resections At least 1 week since prior surgery or biopsy for anaplastic astrocytoma No concurrent surgery (including resection, stereotactic surgery, or interstitial implants) Other: At least 4 weeks since prior investigational agents No other concurrent investigational agents