A phase II trial of ifosfamide in previously untreated children and adolescents with unresectable rhabdomyosarcoma

Background. Children and adolescents with unresectable rhabdomyosarcoma fare poorly when treated with contemporary chemotherapeutic regimens. Evaluation of newly developed agents in these patients is important to improve their outcome. Based on a preclinical rhabdomyosarcoma xenograft model that accurately predicted the activity of new agents, the safety and efficacy of ifosfamide was evaluated as part of a Phase II clinical trial in previously untreated children with unresectable rhabdom yosarcoma. Methods. Twenty‐two children and adolescents (median age, 9 years) with newly diagnosed unresectable rhabdomyosarcoma (Intergroup Rhabdomyosarcoma Study Group III [n = 15] or IV [n = 71] received two courses of ifosfamide at a dose of 1.6 g/m² intravenously for 5 days over a 6‐week period. Then the patients were evaluated for response, and additional treatment with surgery, radiation therapy, and multiagent chemotherapy (vincristine, cyclophosphamide, dactinomycin, and doxorubicin) was administered. Results. Nineteen of 22 patients (86%) had a partial response to ifosfamide given as a single agent. No complete responses to this agent alone were observed. After administration of additional chemotherapy and local control measures (radiation therapy and surgery), the estimated proportion of patients surviving progressionfree at 2 years was 63% (95% confidence interval, 37‐80%). Ifosfamide was tolerated well; the most frequent toxicity was nondose‐limiting myelosuppression. Transient mild renal toxicity infrequently was observed, and no central nervous system toxicity occurred in this group of patients. Conclusions. Ifosfamide appears to have significant clinical activity in untreated patients with unresectable rhabdomyosarcomas. These findings provide an accurate estimate of the response rate to single‐agent ifosfamide in this group of previously untreated patients and thus provide a foundation for its rational incorporation into multiagent clinical trials. In addition, the potential benefits of this type of new drug development were demonstrated. Cancer 1993; 71:2119‐25.