Phase I study of topotecan in combination with cyclophosphamide in pediatric patients with malignant solid tumors: a Pediatric Oncology Group Study.

PURPOSE: To determine the maximum-tolerated dose (MTD) and dose-limiting toxicity of topotecan when combined with cyclophosphamide in pediatric patients with recurrent or refractory malignant solid tumors. PATIENTS AND METHODS: A total of 33 patients received cyclophosphamide (250 mg/m2/dose) followed by topotecan in escalating doses (0.6 to 0.75 mg/m2/dose), each given as a 30-minute infusion daily for 5 days. A total of 154 fully assessable treatment courses were given to these patients.
RESULTS: Neutropenia was the dose-limiting toxicity of the therapy at both topotecan dose levels. The addition of filgrastim allowed escalation of the topotecan dose to the 0.75-mg/m2 level with acceptable neutropenia. Other significant toxicities were anemia and thrombocytopenia. Nonhematopoietic toxicity of grades > or = 3 was not observed. Responses were reported in patients with Wilms' tumor (one complete response [CR], one partial response [PR]), neuroblastoma (one CR, one PR), rhabdomyosarcoma (one PR), and osteosarcoma (one PR). Pharmacokinetic studies indicate that cyclophosphamide administered on the schedule used in this study did not alter topotecan disposition on day 5. As with previous studies, a pharmacodynamic relation between systemic exposure and myelosuppression was noted.
CONCLUSION: The combination of topotecan and cyclophosphamide shows activity in a wide variety of pediatric solid tumors and can be given with acceptable hematopoietic toxicity with the use of filgrastim support. We recommend that pediatric phase II trials use cyclophosphamide 250 mg/m2 followed by topotecan 0.75 mg/m2 daily for 5 days with filgrastim for amelioration of neutropenia.