131I-Metaiodobenzylguanidine Theranostics in Neuroblastoma: Historical Perspectives; Practical Applications

Much efficacy is gained in clinical practice if a single agent can be used for both diagnosis and therapy, a practice termed theranostics. Metaiodobenzylguanidine (mIBG), a norepinephrine analogue with high sensitivity and specificity for neuroblastoma, is an exemplar of theranostics. The physiologic biodistribution of mIBG, with absence of uptake in bone and bone marrow, allows ready detection not only of primary soft tissue tumors but also of disease in bone and marrow, the two most common sites of metastases in those with neuroblastoma. Owing to its increased sensitivity and specificity in disease detection compared to the Technetium-99m methylene diphosphonate bone scan, 123I-mIBG has become the cornerstone of staging and therapeutic response monitoring in patients with neuroblastoma. More recently, semiquantitative scoring systems have been developed to evaluate disease burden and response to treatment based on 123I-mIBG scans. Initial data suggest that the use of these semiquantitative scoring methods has prognostic value in assessing outcomes for patients with high-risk neuroblastoma. When labeled with 131I, mIBG can be used as a systemic therapeutic agent to treat high-risk disease, and to date, over 1000 patients with neuroblastoma have been treated worldwide with this agent. This article reviews the evolution of 131I-mIBG therapy from its initial use as a single therapeutic agent to modern applications involving high-dose chemotherapy and autologous stem-cell transplant as well as its use as a front-line agent in high-risk neuroblastoma.