Cytarabine in Treating Young Patients With Recurrent or Refractory Ewing's Sarcoma

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)