Temozolomide in Treating Patients With Progressive Low-Grade Glioma

DISEASE CHARACTERISTICS: * Histologically confirmed progressive, primary, intracranial, supratentorial, low-grade glioma including: * Astrocytoma * Oligodendroglioma * Mixed glioma * Optic pathway glioma\* * Pontine glioma\* NOTE: \*Biopsy not required * Patients with optic pathway glioma must also meet the following criteria: * Progressive loss of vision as defined by doubling of octaves * Visual acuity loss not explained by other causes * Increase in proptosis of greater than 3 mm * Increase in diameter of optic nerve of at least 2 mm on neuroimaging * Increase in distribution of tumor involving optic tracts or optic radiations as indicated by CT scan or MRI PATIENT CHARACTERISTICS: Age: * 4 and over Performance status: * Karnofsky 70-100% Life expectancy: * More than 12 weeks Hematopoietic: * Absolute neutrophil count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 10 g/dL Hepatic: * Bilirubin less than 1.5 times upper limit of normal (ULN) * SGOT and SGPT less than 2.5 times ULN * Alkaline phosphatase less than 2 times ULN Renal: * Creatinine less than 1.5 times ULN * BUN less than 1.5 times ULN Other: * Must be neurologically stable * No systemic disease * No acute infection requiring IV antibiotics * No frequent vomiting * No other medical condition that would interfere with oral medication (e.g., partial bowel obstruction) * No other prior or concurrent malignancies except: * Surgically cured carcinoma in situ of the cervix * Basal or squamous cell skin cancer * HIV negative * No AIDS-related illness * Not pregnant or nursing * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: * No concurrent biologic therapy (growth factors or epoetin alfa) Chemotherapy: * At least 6 weeks since prior chemotherapy unless evidence of disease progression * No other concurrent chemotherapy Endocrine therapy: * Not specified Radiotherapy: * At least 6 weeks since prior radiotherapy unless evidence of disease progression * No concurrent radiotherapy Surgery: * At least 3 weeks since prior surgery unless evidence of disease progression * Recovered from all prior surgery Other: * No other concurrent investigational drugs