Valproic Acid in Treating Young Patients With Recurrent or Refractory Solid Tumors or CNS Tumors

DISEASE CHARACTERISTICS:

   - Histologically confirmed* malignant solid tumor, including CNS tumors, at original
   diagnosis or relapse

      - Recurrent or refractory disease NOTE: *Histologic confirmation not required for
      intrinsic brain stem or optic pathway tumors

   - Measurable or evaluable disease, defined by 1 of the following criteria:

      - Any unidimensionally measurable lesion ≥ 10 mm by standard MRI or CT scan for
      either solid or CNS tumors

      - At least 1 nonmeasurable lesion that is evaluable by nuclear medicine,
      immunocytochemistry, tumor markers, cerebrospinal fluid cytology, or other
      reliable measures

   - No known curative therapy exists

   - No documented tumor involvement in the bone marrow

PATIENT CHARACTERISTICS:

Age

   - 2 to 21

Performance status*

   - Lansky 50-100% (for patients ≤ 10 years of age)

   - Karnofsky 50-100% (for patients > 10 years of age)

Life expectancy

   - Not specified

Hematopoietic

   - Absolute neutrophil count ≥ 1,000/mm^3

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

   - Hemoglobin ≥ 8.0 g/dL (transfusions allowed)

Hepatic

   - Bilirubin ≤ 1.5 times upper limit of normal (ULN)

   - ALT ≤ 110 (ULN for this study is 45 U/L)

   - Albumin ≥ 2 g/dL

Renal

   - Creatinine clearance or radioisotope glomerular filtration rate ≥ 70 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 over 15 years of age)

Other

   - Not pregnant or nursing

   - Negative pregnancy test

   - Fertile patients must use effective contraception

   - Neurologic deficits in patients with CNS tumors must be stable for ≥ 1 week before
   study entry

   - No uncontrolled infection

   - No known urea cycle disorders or other metabolic disorders

   - No other condition that would preclude study compliance

PRIOR CONCURRENT THERAPY:

Biologic therapy

   - Recovered from prior immunotherapy

   - At least 7 days since prior hematopoietic growth factors that support platelet or WBC
   number or function

   - At least 7 days since prior antineoplastic biologic agents

   - At least 3 months since prior stem cell transplantation or rescue without total body
   irradiation

      - No evidence of active graft vs host disease

   - No other concurrent anticancer biologic therapy or immunotherapy

Chemotherapy

   - More than 3 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas)
   and recovered

   - No other concurrent anticancer chemotherapy

Endocrine therapy

   - Patients with CNS tumors must be on a stable or decreasing dose of dexamethasone for
   the past 7 days

Radiotherapy

   - See Biologic therapy

   - Recovered from prior radiotherapy

   - At least 6 months since prior total body irradiation, craniospinal radiotherapy, or
   radiotherapy to ≥ 50% of the pelvis

   - At least 6 weeks since other prior substantial bone marrow radiotherapy

   - At least 2 weeks since prior local palliative small port radiotherapy

   - No concurrent anticancer radiotherapy

Surgery

   - Not specified

Other

   - No other concurrent investigational agents

   - No other concurrent anticancer agents

   - No other concurrent anticonvulsants

      - Patients receiving valproic acid (VPA) before study entry must have a total
      trough VPA concentration < 100 mcg/mL within the past 7 days