DISEASE CHARACTERISTICS:

• Histologically confirmed Ewing's sarcoma or primitive neuroectodermal tumor (PNET)

• Disease that has recurred or not responded despite prior therapy

  • Has declined enrollment on or is not eligible for clinical trial COG-AEWS0521
• Must have at least one site of measurable disease involving lung or soft tissue as documented by CT scan and/or MRI
• No disease limited to bone

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)
• Life expectancy ≥ 8 weeks
• ANC ≥ 750/mm^3
• Platelet count ≥ 75,000/mm^3 (50,000/mm^3 if documented bone marrow metastatic disease) (transfusion independent)
• Hemoglobin ≥ 8.0 g/dL (red blood cell transfusions allowed)
• Bilirubin ≤ 1.5 times upper limit of normal (ULN) for age and < 2.0 mg/dL
• ALT ≤ 2.5 times ULN

• Creatinine clearance or radioisotope GFR ≥ 70 mL/min OR creatinine meeting the following criteria:

  • ≤ 0.4 mg/dL (1 month to < 6 months of age)
  • ≤ 0.5 mg/dL (6 months to < 1 year of age)
  • ≤ 0.6 mg/dL (1 to < 2 years of age)
  • ≤ 0.8 mg/dL (2 to < 6 years of age)
  • ≤ 1.0 mg/dL (6 to < 10 years of age)
  • ≤ 1.2 mg/dL (10 to < 13 years of age)
  • ≤ 1.4 mg/dL (≥ 13 years of age) (female)
  • ≤ 1.5 mg/dL (13 to < 16 years of age) (male)
  • ≤ 1.7 mg/dL (≥ 16 years of age) (male)
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No uncontrolled infection, including systemic fungal infections requiring ongoing antifungal therapy

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• Recovered from all prior tumor-directed therapy
• At least 7 days since prior biologic therapy or immunotherapy
• At least 1 week since prior hematopoietic growth factors (2 weeks for pegfilgrastim)
• At least 2 weeks since prior myelosuppressive chemotherapy
• At least 2 weeks since prior local palliative (small-port) radiotherapy
• At least 6 weeks since prior substantial bone marrow radiotherapy
• At least 6 months since prior radiotherapy to ≥ 50% of the pelvis
• At least 6 months since prior autologous stem cell transplantation
• No prior allogeneic stem cell transplantation
• No prior cytarabine
• No other concurrent investigational agents, including chemotherapy, immunotherapy, or biologic therapy

• No other concurrent anticancer chemotherapy or immunomodulating agents

  • Concurrent corticosteroids allowed
• No concurrent intrathecal chemotherapy
• Concurrent radiotherapy to localized painful lesions allowed provided at least one measurable lesion is not irradiated (no irradiated lesion may be used to assess tumor response)