Radioiodinated Metaiodobenzylguanidine Treatment of Neuroendocrine Tumors in Adults

Metaiodobenzylguanidine (MIBG), radioiodinated with I-131, has been available for 25 years. Its role in the United States is limited to diagnostic imaging, whereas its therapeutic application in patients with neuroendocrine tumors for whom surgical treatment would not lead to a cure, has been approved in Europe. I-131-MIBG treatments can be a valuable addition to the current gamut of treatment options for patients with metastatic neuroendocrine tumors, especially given the limited role for other systemic treatments, such as chemotherapy. There are basically two treatment strategies: one or two high-dose treatments or continuous low-dose treatments. I-131-MIBG could induce symptomatic relief in the vast majority of patients treated, both following high-dose treatment and low-dose maintenance treatment. Biochemical responses can be observed in about half of the patients, whereas radiographic responses are described in roughly one third of the patients. Several articles suggested a survival benefit to patients treated with I-131-MIBG. Side-effects of the treatment mainly consist of myelotoxicity, nausea, and hypothyroidism. Future developments are focused on the use of high-specific-activity I-131-MIBG in high doses. The role of I-131-MIBG in relation to other treatments remains to be established, although treatment I-131-MIBG seems to be at least as effective as other systemic treatments, with limited side-effects.