Cyclophosphamide plus topotecan in children with recurrent or refractory solid tumors: a Pediatric Oncology Group phase II study.

To determine the response rate of the combination of cyclophosphamide and topotecan in pediatric patients with recurrent or refractory malignant solid tumors. A total of 91 pediatric patients, 83 of whom were fully assessable for response and toxicity, received cyclophosphamide (250 mg/m2/dose) followed by topotecan (0.75 mg/m2/dose), each given as a 30-minute infusion daily for 5 days. All patients received filgrastim (5 mcg/kg) daily until the absolute neutrophil count (ANC) was > or = 1,500 microL after the time of the expected ANC nadir. A total of 307 treatment courses were given to the 83 fully assessable patients. Responses (complete response plus partial response) were seen in rhabdomyosarcoma (10 of 15 patients), Ewing's sarcoma (six of 17 patients), and neuroblastoma (six of 13 patients). Partial responses were seen in two of 18 patients with osteosarcoma and in one patient with a Sertoli-Leydig cell tumor. Twenty-three patients had either minor responses (n = 6) or stable disease (n = 17); the median number of courses administered to patients with partial or complete response was six (range, two to 13 courses), and the median administered to those with stable disease was three (range, one to 11 courses). The toxicity of the combination was limited principally to the hematopoietic system. Of 307 courses, 163 (53%) were associated with grade 3 or 4 neutropenia, 84 (27%) with grade 3 or 4 anemia, and 136 (44%) with grade 3 or 4 thrombocytopenia. Despite the severe myelosuppression, only 34 (11%) of 307 courses were associated with grade 3 or 4 infection. Nonhematopoietic toxicity of grades > or = 3 was rare and consisted of nausea and vomiting (two courses), perirectal mucositis (one course), transaminase elevation (one course), and hematuria (two courses). The combination of cyclophosphamide and topotecan is active in rhabdomyosarcoma, neuroblastoma, and Ewing's sarcoma. Stabilization of disease was seen in osteosarcoma, although objective responses were rare in this disease. The therapy can be given with acceptable hematopoietic toxicity with the use of filgrastim support.