Nuclear medicine therapy of pheochromocytoma and paraganglioma.

Pheochromocytomas and paragangliomas are rare catecholamine-producing tumors which arise from chromaffin tissue. When a pheochromocytoma/paraganglioma is suspected, biochemical confirmation is based on 24-hour urinary excretion rates of catecholamines and their metabolites (metanephrines, VMA, etc.). Following biochemical confirmation non invasive imaging techniques such as CT and/or MR of the abdomen and 123I-MIBG scintigraphy are performed to localize the tumor. 111In-octreotide may also be applied, mainly to localize head and neck chemodectomas. Malignant paragangliomas of either adrenal or extra-adrenal origin show a variable natural history: from a locally invasive indolent tumor to a highly aggressive malignancy. Surgery with complete resection or debulking of the primary tumor is the standard treatment. External radiotherapy and chemotherapy are usually scarcely effective. An alternative treatment is 131I-MIBG therapy which is performed with high specific activity 131I-MIBG. Usually a standardized dose ranging from 3.7 to 9.1 GBq of 131I-MIBG is administered by slow i.v. infusion. In advanced stage cases 131I-MIBG therapy aims at symptom palliation and tumor function reduction as well as at tumor arrest or tumor regression. In these cases MIBG therapy allows prolonged survival and good quality of life. In less advanced cases the purpose of MIBG therapy is to complement surgery and to achieve the total eradication of the tumor. Non functioning malignant paraganglioma can some time also concentrate MIBG and can be treated with high doses of the tracer. 131I-MIBG therapy is a safe treatment and is usually well tolerated by the patient (with rather low myelotoxicity).