Inclusion Criteria:

1. Patients must be less than 22 years of age inclusive

2. Tumor histologies: medulloblastoma/PNET, neuroblastoma, sarcomas, and other pediatric
solid tumors for which there is no known effective therapy.

3. Patients must have measurable disease, documented by clinical, radiographic, or
histologic criteria.

4. Patients must have a performance status of 0, 1 or 2. Use Karnofsky for patients >
16 years of age and Lansky for patients <= 16 years of age.

5. Patients must have a life expectancy of >= 8 weeks.

6. Prior Therapy: Patients must have fully recovered from the acute toxic effects of all
prior chemotherapy, immunotherapy, or radiotherapy prior to entering this study.

7. Patients must not be taking the following medications: growth factors, steroids, and
CYP3A4 inducers or inhibitors.

8. Patients must have adequate bone marrow, renal, liver function, pulmonary, or central
nervous system function.

9. Must be able and willing to participate in all study procedures, including the ERMBT
and pharmacokinetic studies.

10. All patients and/or their parents or legal guardians must sign a written informed
consent. (11) All institutional, FDA, and NCI requirements for human studies must be
met.

Exclusion Criteria:

1. Males or females of reproductive potential may not participate unless they have
agreed to use an effective contraceptive method.

2. Patients with an uncontrolled infection.

3. Allergy to erythromycin

4. Patients who have previously received either cyclophosphamide or topotecan are
eligible for this study.