Purpose: The analogue 131I-metaiodobenzylguanidine (MIBG), which is specifically targeted to neuroblastoma cells, may provide more effective and less toxic treatment for neuroblastoma than conventional external-beam radiotherapy. We report a dose escalation study of 131I-MIBG to define dose-limiting toxicity without and with autologous bone marrow support.
Patients and methods: Thirty patients with relapsed neuroblastoma were treated in groups of six with escalating doses of 3 to 18 mCi/kg of 131I-MIBG. After rapid escalation in the first three patients treated at 3 to 6 mCi/kg, treatment was escalated in 3-mCi/kg increments from 9 to 18 mCi/kg. Autologous tumor-free bone marrow was cryopreserved in all patients receiving 12 mCi/kg and more. Toxicity and response were assessed.
Results: Eighty percent of patients who received 12 mC/kg or more experienced grade 4 thrombocytopenia and/or neutropenia. Dose-limiting hematologic toxicity was reached at 15 mCi/kg, at which level two of five assessable patients required bone marrow reinfusion for absolute neutrophil count (ANC) of less than 200/microL for more than 2 weeks, and four of nine at the 18-mCi/kg level. Prolonged thrombocytopenia was common, with failure to become platelet-transfusion independent in nine patients. One patient with extensive prior treatment developed secondary leukemia and three became hypothyroid. Responses were seen in 37% of patients, with one complete response (CR), 10 partial response (PR), three mixed response, 10 stable disease, and six progressive disease. The minimum dose of 131I-MIBG for 10 of the 11 responders was 12 mCi/kg.
Conclusion: Treatment with 131I-MIBG has mainly hematologic toxicity, which can be abrogated with bone marrow rescue. The high response rate in refractory disease suggests that this agent may be useful in combination with myeloablative chemotherapy and autologous stem-cell rescue to improve outcome in advanced neuroblastoma.