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