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