Meta[131I]iodobenzylguanidine therapy for patients with metastatic and unresectable pheochromocytoma and paraganglioma

Abstract Introduction Pheochromocytomas (PHEOs) and paragangliomas (PGLs) are tumors that can exhibit a malignant behavior. Targeted radiotherapy with 131 I-metaiodobenzylguanidine ( 131 I-MIBG) has proven useful in patients with unresectable, metastatic and/or relapsed disease. Methods We review the literature and our experience at UCSF to highlight important characteristics of PHEO/PGL and the use of 131 I-MIBG in the treatment of this disease. Results These tumors are rare, with a diagnosed incidence of only two to four cases per million annually; 40% are discovered at autopsy. Clinical manifestations are caused by excess secretion of catecholamines, although some PGLs are nonsecretory. Approximately 25% of patients with PHEO/PGLs have an underlying genetic predisposition. The risk of a germline mutation is higher in children. Diagnostic evaluation should include serial determinations of fractionated metanephrines and serum chromogranin A. Staging requires both 123 I-MIBG and full-body magnetic resonance imaging or 18 FDG-PET scanning. The primary treatment for PHEO/PGL is resection. Patients may be candidates for treatment with 131 I-MIBG if they have unresectable or metastatic tumors that are avid for MIBG. Such patients usually respond to this targeted radioisotope therapy and many achieve a durable remission. Myelosuppression is a dose-related side effect that can be treated with transfusions or autologous hematopoietic stem cells. Late side effects can include infertility, myelodysplasia and second cancers. Conclusions Treatment with 131 I-MIBG can be considered for patients if surgery is not feasible. There are significant risks associated with this treatment, but the majority of patients will respond. Treatment with 131 I-MIBG should be done at institutions with experience in delivering targeted radiotherapeutics.