Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically proven malignancy, including but not limited to, any of the following:

- Patients with MRI findings in keeping with a diffuse intrinsic pontine glioma
will be eligible without histological confirmation of tumor type

- Patients with a diagnosis of diffuse intrinsic pontine glioma who are not
eligible for the erlotinib hydrochloride phase I study (CCLG-NAG-2005-09)

- Patients with relapsed ependymoma following the CCLG phase II study of
intravenous etoposide (CCLG-CNS-2001-4) or prior to this are eligible at the
discretion of the physician

- Patients with relapsed osteogenic sarcoma, other soft tissue sarcomas, or other
solid tumors may be suitable for this study at the discretion of the physician

- Radiologically evaluable disease without bone marrow involvement

PATIENT CHARACTERISTICS:

Inclusion criteria:

- Lansky performance status (PS) 30-100% (for patients ≤ 12 years of age)

- ECOG PS ≤ 2 (for patients ≥ 13 years of age)

- Life expectancy ≥ 9 weeks

- ANC > 1,000/mm³

- Platelet count > 100,000/mm³

- Hemoglobin > 9 g/dL

- Serum creatinine ≤ 1.5 times upper limit of normal (ULN) for age

- Serum total bilirubin normal

- AST or ALT ≤ 2 times ULN

- Glomerular filtration rate ≥ 60 mL/min

- Negative pregnancy test

- Fertile patients must use effective contraception

Exclusion criteria:

- Poor medical risk because of nonmalignant systemic disease or uncontrolled infection

- Concurrent malignancies at other sites

PRIOR CONCURRENT THERAPY:

Inclusion criteria:

- Prophylactic trimethoprim-sulfamethoxazole must be stopped 1 week prior to
methotrexate administration

Exclusion criteria:

- Received chemotherapy or biologic therapy within the past 4 weeks

- Received radiotherapy within the past 6 weeks