Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed malignancy that is relapsed or refractory to conventional
therapy at original diagnosis including:

- Brain tumors

- Gliomas or astrocytomas

- Medulloblastomas or primitive neuroectodermal tumor (PNET) in CNS

- (Brain tumor stratum closed to accrual effective 07/02/2001)

- Sarcomas

- Soft tissue sarcoma (undifferentiated sarcoma, embryonal or alveolar
rhabdomyosarcoma (RMS), or non-RMS soft tissue sarcoma)

- Osteosarcoma

- Ewing's sarcoma/peripheral PNET tumors

- Neuroblastoma

- (Neuroblastoma stratum closed to accrual effective 07/02/2001)

- Histology requirement waived for brain stem tumors (Brain tumor stratum closed to
accrual effective 07/02/2001)

- Measurable disease documented by clinical, radiographic, or histologic criteria

- Lesions in previously irradiated fields may be used to assess tumor response if there
has been evidence of subsequent tumor growth in those fields

- No bone marrow metastases with granulocytopenia and/or thrombocytopenia

PATIENT CHARACTERISTICS:

Age:

- 30 days to 21 years at diagnosis

Performance status:

- ECOG 0-2

Life expectancy:

- More than 2 months

Hematopoietic:

- Absolute neutrophil count at least 1,000/mm3

- Hemoglobin at least 10.0 g/dL (may receive RBC transfusions)

- Platelet count at least 100,000/mm3 (50,000/mm3 if post bone marrow transplantation)
(transfusion independent)

Hepatic:

- Bilirubin no greater than 1.5 times normal

- SGOT or SGPT less than 2.5 times normal

Renal:

- Creatinine no greater than 1.5 times normal OR

- Creatinine clearance or radioisotope glomerular filtration rate at least 70 mL/min

Neurologic:

- No greater than grade 2 CNS toxicity OR

- Stable CNS status for brain tumors (Brain tumor stratum closed to accrual effective
07/02/2001)

- Seizure disorders allowed if well-controlled with anticonvulsants

Other:

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

- At least 3 months since prior bone marrow transplantation and recovered

- At least 2 weeks since prior cytokines and recovered

- No concurrent filgrastim (G-CSF) or other cytokines

- No concurrent immunomodulating agents

Chemotherapy:

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

- No prior topotecan or other camptothecins

- No other concurrent anticancer chemotherapy

Endocrine therapy:

- Concurrent corticosteroids for CNS tumors with increased intracranial pressure
allowed (Brain tumor stratum closed to accrual effective 07/02/2001)

Radiotherapy:

- At least 2 months since prior craniospinal radiotherapy or radiotherapy to more than
50% of the bone marrow and recovered

- Concurrent radiotherapy to localized painful lesions allowed provided that at least 1
measurable lesion is not irradiated

Other:

- Recovered from any other prior therapy