DISEASE CHARACTERISTICS: - Newly diagnosed diffuse intrinsic pontine gliomas (defined as tumors with a pontine epicenter and diffuse involvement of ≥ 2/3 of the pons) - Patients with brainstem tumors that do not meet these criteria or are not considered to be typical intrinsic pontine gliomas are eligible provided their tumors are biopsied and proven to be an anaplastic astrocytoma, glioblastoma multiforme, gliosarcoma, or anaplastic mixed glioma - No patients with juvenile pilocytic astrocytoma, fibrillary astrocytoma, gangliogliomas, or other mixed gliomas without anaplasia - No patients with disseminated disease (MRI of the spine must be performed if disseminated disease is suspected by the treating physician) PATIENT CHARACTERISTICS: - Karnofsky performance status (PS) 50-100% (for patients > 16 years of age) or Lansky PS 50-100% (for patients ≤ 16 years of age) - Patients who are unable to walk because of paralysis, but who are up in a wheelchair, will be considered ambulatory for the purpose of assessing the performance status - ANC ≥ 1,000/mm^3 - Platelet count ≥ 100,000/mm^3 (transfusion independent, defined as not receiving platelet transfusions within the past 7 days) - Hemoglobin ≥ 8.0 g/dL (RBC transfusions allowed) - Creatinine clearance or radioisotope GFR ≥ 70 mL/min OR a serum creatinine based on age/gender as follows: - ≤ 0.8 mg/dL (for patients 3 to < 6 years of age) - ≤ 1 mg/dL (for patients 6 to < 10 years of age) - ≤ 1.2 mg/dL (for patients 10 to < 13 years of age) - ≤ 1.4 mg/dL (for female patients ≥ 13 years of age) - ≤ 1.5 mg/dL (for male patients 13 to < 16 years of age) - ≤ 1.7 mg/dL (for male patients ≥ 16 years of age) - Bilirubin (sum of conjugated + unconjugated) ≤ 1.5 times upper limit of normal (ULN) for age - ALT ≤ 110 U/L (for the purpose of this study, the ULN for ALT is 45 U/L) - Serum albumin ≥ 2 g/dL - Not pregnant or nursing - Negative pregnancy test - Fertile patients must use effective contraception - Able to swallow capsules or liquids - Not dependent on NG tube feeding - Patients with seizure disorder are eligible provided that they are not on enzyme-inducing anticonvulsants and seizures are well controlled - No uncontrolled infection - No patients who, in the opinion of the investigator, may not be able to comply with the safety monitoring requirements of the study PRIOR CONCURRENT THERAPY: - No prior treatment except for dexamethasone and/or surgery - At least 2 weeks since prior valproic acid - More than 7 days since prior growth factors that support platelet or white cell number or function - No other concurrent investigational drugs - No other concurrent anticancer agents (including chemotherapy, immunotherapy, or biologic therapy) - No concurrent coumadin, heparin, low-molecular weight heparin, or any other anticoagulants - No concurrent aspirin (> 81 mg/day), NSAIDs, clopidogrel (Plavix), dipyridamole (Persantine), or any other drug that inhibits platelet function - No concurrent enzyme-inducing anticonvulsants