Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed high-grade glioma, including any of the following:

- Glioblastoma multiforme

- Anaplastic astrocytoma

- Anaplastic oligodendroglioma

- Anaplastic mixed oligoastrocytoma

- Malignant astrocytoma not otherwise specified

- Patients with clinical and radiographic diagnosis of brain stem glioma are
also eligible

- Evidence of tumor progression by MRI or CT scan

- Scan must be performed while patient is on a stable steroid dose for at least 5
days

- Must have failed prior radiotherapy

- Residual disease after prior resection of recurrent or progressive tumor is allowed

PATIENT CHARACTERISTICS:

Age

- 18 and over

Performance status

- Karnofsky 60-100%

Life expectancy

- More than 8 weeks

Hematopoietic

- Absolute neutrophil count greater than 1,500/mm^3

- Platelet count at least 100,000/mm^3 (transfusion independent)

- Hemoglobin at least 10 g/dL (transfusion allowed)

Hepatic

- Bilirubin less than 2 times upper limit of normal (ULN)

- SGOT less than 2 times ULN

- No significant active hepatic disease

Renal

- Creatinine less than 1.5 mg/dL OR

- Creatinine clearance at least 60 mL/min

- No significant active renal disease

Cardiac

- No significant active cardiac disease

Other

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use 2 effective methods of contraception during and for 2
months after study participation

- Able to swallow whole capsules

- No active infection requiring IV antibiotics

- No significant active psychiatric disease that would preclude use of the study drug

- No other significant uncontrolled medical illness that would preclude study
participation

- No other active life-threatening malignancy

PRIOR CONCURRENT THERAPY:

Biologic therapy

- At least 1 week since prior interferon or thalidomide

- No concurrent anticancer immunotherapy

Chemotherapy

- At least 2 weeks since prior vincristine

- At least 3 weeks since prior procarbazine

- At least 6 weeks since prior nitrosoureas

- No other concurrent anticancer chemotherapy

Endocrine therapy

- See Disease Characteristics

- At least 1 week since prior tamoxifen

- Concurrent steroids for the control of increased intracranial pressure allowed

Radiotherapy

- See Disease Characteristics

- At least 4 weeks since prior radiotherapy

- No concurrent anticancer radiotherapy

Surgery

- See Disease Characteristics

- Prior recent resection of recurrent or progressive disease allowed

Other

- Recovered from all prior therapy

- At least 1 week since prior noncytotoxic agents (e.g., isotretinoin), except for
radiosensitizers

- At least 4 weeks since prior investigational agents

- At least 4 weeks since prior cytotoxic therapy

- No other concurrent investigational agents