DISEASE CHARACTERISTICS:

• Histologically confirmed supratentorial malignant glioma, including any of the following:

  • Glioblastoma multiforme
  • Gliosarcoma
  • Anaplastic astrocytoma
  • Anaplastic oligodendroglioma
  • Anaplastic mixed oligoastrocytoma
  • Malignant glioma/astrocytoma not otherwise specified OR
• Clinical and radiographic diagnosis of progressive low-grade glioma
• Radiographically diagnosed infiltrating brain stem gliomas not amenable to biopsy allowed

• Recurrent or progressive disease as determined by 1 of the following:

  • CT scan or MRI within the past 21 days
  • Biopsy within the past 12 weeks
• Failed prior radiotherapy

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• Karnofsky 60-100%

Life expectancy

• More than 8 weeks

Hematopoietic

• Granulocyte count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3 (transfusion independent)
• Hemoglobin at least 8 g/dL (transfusion allowed)

Hepatic

• Bilirubin no greater than 1.5 mg/dL
• AST and ALT no greater than 2 times upper limit of normal
• No significant active hepatic disease that would preclude study participation

Renal

• Creatinine no greater than 1.5 mg/dL OR
• Creatinine clearance at least 60 mL/min
• No significant active renal disease that would preclude study participation

Cardiovascular

• No significant active cardiac disease that would preclude study participation

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception during and for 2 months after study participation
• No other malignancy within the past 3 years except nonmelanoma skin cancer or carcinoma in situ of the cervix
• No significant active psychiatric disease that would preclude study participation
• No other condition or laboratory abnormality that would preclude study participation
• Able to swallow capsules whole

PRIOR CONCURRENT THERAPY:

Biologic therapy

• At least 2 weeks since prior interferon
• No concurrent immunotherapy

Chemotherapy

• At least 2 weeks since prior vincristine
• At least 3 weeks since prior procarbazine
• At least 4 weeks since prior temozolomide or carboplatin
• At least 6 weeks since prior nitrosoureas
• No other concurrent anticancer chemotherapy

Endocrine therapy

• At least 2 weeks since prior tamoxifen
• Concurrent steroids allowed provided dose has been stable for at least 5 days prior to study enrollment

Radiotherapy

• See Disease Characteristics
• At least 2 weeks since prior radiotherapy
• No concurrent radiotherapy

Surgery

• At least 2 weeks since prior resection of a recurrent or progressive tumor

Other

• At least 2 weeks since other prior non-cytotoxic therapy
• At least 4 weeks since other prior cytotoxic therapies
• More than 28 days since prior experimental study drugs
• No other concurrent investigational agents