A Pharmacokinetic Study of Oral Cyclophosphamide and Topotecan in Children With Recurrent Solid Tumors

Overview

The purposes of this study include: * Determination of the change in clearance of topotecan and topotecan lactone between day 1 and day 14 for patients receiving treatment with p.o. topotecan and p.o. cyclophosphamide x 14 days. * Determination of the correlation between the activity of CYP3A4, as measured by the 14C- Erythromycin Breath Test (ERMBT), and topotecan/topotecan lactone clearance for patients receiving treatment with p.o. topotecan and p.o. cyclophosphamide x 14 days. * Determination of the response rate to oral cyclophosphamide and oral topotecan in recurrent and/or refractory pediatric solid tumors. * Obtain additional safety data for the chemotherapy regimen, p.o. topotecan and p.o. cyclophosphamide x 14 days. * Report the frequency of severe toxicities associated with the level of CYP3A4 activity, as measured by the ERMBT, for patients receiving treatment with p.o. topotecan and p.o. cyclophosphamide x 14 days.

Upon obtaining informed consent, patients will begin two courses of oral cyclophosphamide and topotecan x 14 days. During the first of two courses, patients will perform the 14C-Erythromycin Breath Test and have topotecan pharmacokinetics performed on day 1 and 14. The subjects will also have various medical tests and procedures performed that are part of regular cancer care which include: Medical history and physical examination to be done weekly, blood tests to be done weekly, heart and kidney function tests, various scans to be done after two courses of treatment, and a pregnancy test for females of childbearing age to be done prior to starting treatment. Patients may continue to receive additional courses of oral cyclophosphamide and topotecan provided that they do not experience tumor progression or intolerable side effects.