Inclusion Criteria:

- Histologically confirmed solid tumors including the following:

- Ewing's sarcoma

- Bone or soft tissue primitive neuroectodermal tumor

- Osteosarcoma

- Neuroblastoma

- Desmoplastic small round cell tumor

- Synovial cell sarcoma

- Gastrointestinal stromal tumor (GIST)

- Metastatic pulmonary disease eligible

- No pleural effusion of any size or definite radiologic evidence of pleural-based
disease

- Recurrent or refractory to conventional therapy

- GIST eligible at initial presentation

- Tumor tissue blocks must be available

- At least 1 measurable lesion

- At least 20 mm by conventional techniques

- At least 10 mm by spiral CT scan

- Lesions assessable only by radionuclide scan are not considered measurable

- Performance status - Lansky 50-100% (≤ 10 years of age)

- Performance status - Karnofsky 50-100% (> 10 years of age)

- At least 2 months

- Absolute neutrophil count ≥ 1,000/mm^3*

- Platelet count ≥ 75,000/mm^3* (transfusion independent)

- Hemoglobin ≥ 8.0 g/dL* (RBC transfusions allowed)

- Bilirubin ≤ 1.5 times upper limit of normal (ULN)

- ALT ≤ 2.5 times ULN

- INR < 1.5

- PTT ≤ ULN

- Fibrinogen ≥ lower limit of normal

- Creatinine normal for age

- Glomerular filtration rate ≥ 70 mL/min

- No uncontrolled infection

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective barrier contraception

- At least 1 week since prior biologic therapy or immunotherapy and recovered

- At least 1 week since prior growth factors

- No concurrent immunomodulating agents

- At least 2 weeks since prior myelosuppressive chemotherapy (4 weeks for nitrosoureas)
and recovered

- No concurrent chemotherapy

- No concurrent steroids

- Recovered from prior radiotherapy

- At least 2 weeks since prior local palliative radiotherapy (small port)

- At least 3 months since prior craniospinal radiotherapy or radiotherapy to 50% or
more of pelvis

- At least 6 weeks since other prior substantial bone marrow radiation

- No concurrent radiotherapy during first course of treatment

- Concurrent palliative radiotherapy to local painful lesions allowed after first
course of treatment provided there is no evidence of disease progression and at least
1 measurable lesion remains outside radiation port

- No concurrent therapeutic doses of warfarin

- No concurrent anticonvulsants that induce the cytochrome p450 enzyme system (e.g.,
phenytoin, carbamazepine, and phenobarbital)

- Concurrent benzodiazepines and gabapentin allowed

- Concurrent low-molecular weight heparin allowed