DISEASE CHARACTERISTICS:

• Histologically confirmed* high-grade glioma or brain stem tumor, including any of the following:

  • Anaplastic astrocytoma
  • Glioblastoma multiforme
  • Anaplastic oligodendroglioma
  • Anaplastic ganglioma
  • Gliosarcoma NOTE: *Histologic confirmation not required for brain stem tumors

• Recurrent or progressive disease after treatment with standard therapy

  • Radiotherapy allowed if considered standard treatment for primary or salvage therapy in advanced of a phase II regimen for the respective disease and presentation
  • No more than 2 recurrences or progressions

• Bi-dimensionally measurable disease, defined as at least 1 lesion that can be measured in ≥ 2 dimensions

  • Diffuse meningeal involvement is not considered measurable disease

PATIENT CHARACTERISTICS:

Performance status

• Karnofsky 60-100% (for patients > 16 years of age) OR
• Lansky 60-100% (for patients ≤ 16 years of age)

Life expectancy

• Not specified

Hematopoietic

• Absolute neutrophil count > 1,500/mm^3
• Platelet count > 100,000/mm^3 (unsupported)
• Hemoglobin > 8 g/dL (may be supported)
• Absolute lymphocyte count ≥ 500/mm^3

Hepatic

• SGOT and SGPT ≤ 2.5 times upper limit of normal (ULN)
• Bilirubin ≤ 1.5 times ULN
• No overt hepatic disease

Renal

• Creatinine clearance ≥ 60 mL/min OR

• Creatinine based on age as follows:

  • No greater than 0.8 mg/dL (for patients ≤ 5 years of age)
  • No greater than 1.0 mg/dL (for patients 6 to 10 years of age)
  • No greater than 1.2 mg/dL (for patients 11 to 15 years of age)
  • No greater than 1.5 mg/dL (for patients > 15 years of age)
• No overt renal disease

Cardiovascular

• No overt cardiac disease

Pulmonary

• No overt pulmonary disease

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No history of severe toxicity (≥ grade 3) associated with temozolomide
• No history of hypersensitivity to dacarbazine, temozolomide, or polyethylene glycol (PEG)
• No infection
• No uncontrolled significant systemic illness
• HIV negative

PRIOR CONCURRENT THERAPY:

Biologic therapy

• At least 3 weeks since prior biologic therapy
• At least 6 months since prior allogeneic bone marrow transplantation
• At least 3 months since prior autologous bone marrow or stem cell transplantation
• At least 2 weeks since prior colony-stimulating factors (e.g., filgrastim [G-CSF], sargramostim [GM-CSF], or erythropoietin)

Chemotherapy

• At least 3 weeks since prior myelosuppressive anticancer chemotherapy (6 weeks for nitrosoureas)
• Prior temozolomide allowed

Endocrine therapy

• Concurrent corticosteroid therapy allowed

Radiotherapy

• See Disease Characteristics
• At least 3 months since prior craniospinal irradiation
• At least 3 months since prior primary tumor local irradiation

Other

• Recovered from all prior therapy
• At least 1 week since prior nonmyelosuppressive investigational agents or anticancer drugs
• No other concurrent anticancer or investigational therapy