O6-Benzylguanine and Temozolomide in Treating Young Patients With Recurrent or Progressive Gliomas or Brain Stem Tumors

INCLUSION CRITERIA * Tumor: Participants must have a high-grade glioma (including e.g. histologically confirmed anaplastic astrocytoma, glioblastoma multiforme, anaplastic oligodendroglioma, anaplastic ganglioma, gliosarcoma) or a brainstem tumor (histologic confirmation waived) with documentation of disease recurrence or progression after treatment with standard therapy. Participants must have bi-dimensionally measurable disease, defined as at least 1 lesion that can be measured in ≥ 2 dimensions * Age: 21 years of age or less * 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: Must have adequate bone marrow function defined as absolute neutrophil count \> 1,500/mm\^3, platelet count \> 100,000/mm\^3 (unsupported), hemoglobin \> 8 g/dL (may be supported), and absolute lymphocyte count ≥ 500/mm\^3 * Hepatic: Must have SGOT and SGPT ≤ 2.5 times upper limit of normal (ULN), bilirubin ≤ 1.5 times ULN, and no overt hepatic disease * Renal: Participants must have 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), or no greater than 1.5 mg/dL (for patients \> 15 years of age). There must be no overt renal disease * Cardiovascular: Must have no overt cardiac disease * Pulmonary: Must have no overt pulmonary disease * Other: Female participants of childbearing potential must have a negative pregnancy test prior to study registration, and must avoid breast-feeding. Female and male participants of childbearing or child-fathering potential must use effective contraception * Bone Marrow Transplant: Must be at least 6 months since prior allogeneic bone marrow transplantation and at least 3 months since prior autologous bone marrow or stem cell transplantation * Growth Factors: Must be at least 2 weeks since prior colony-stimulating factors (e.g., filgrastim \[G-CSF\], sargramostim \[GM-CSF\], or erythropoietin) * Prior Chemotherapy: Must have received last dose of myelosuppressive anticancer chemotherapy ≥ 3 weeks prior to study registration and ≥ 6 weeks for nitrosoureas. Must have received last dose of nonmyelosuppressive investigational agents or anticancer drugs ≥ 7 days prior to study registration. Participants who have received prior temozolomide are eligible * Concurrent Endocrine Therapy: Concurrent corticosteroid therapy is allowed * Prior Radiotherapy: Must have received last fraction of craniospinal irradiation and local irradiation to the primary tumor ≥ 12 weeks prior to study registration * Prior Therapy-Other: Must have recovered from all prior therapy EXCLUSION CRITERIA * Must not have history of severe toxicity (≥ grade 3) associated with temozolomide * Must not be receiving other concurrent anticancer or investigational therapy * Must not have history of hypersensitivity to dacarbazine, temozolomide, or polyethylene glycol (PEG) * Must not have uncontrolled significant systemic illness including infection, or overt renal, hepatic, cardiac, or pulmonary disease * Must not be HIV positive