MIBG for diagnosis and therapy of medullary thyroid carcinoma: is there still a role?

Medullary thyroid carcinoma (MTC) is a relatively rare neuroendocrine tumour originating from the parafollicular C cells and releases calcitonin (hCt), carcinoembryonic antigen (CEA) and occasionally other substances. In 20-30% of cases MTC presents a germline mutation of the RET proto-oncogene and occurs in 3 different hereditary forms: familial MTC, multiple endocrine neoplasia (MEN) 2A and MEN 2B syndrome. Prognosis of MTC is largely related to tumour extension at disease onset. Surgery remains the most effective therapy for potential cure. Overall survival is strictly linked to the occurrence of relapse. After surgery, serum hCt remains the most sensitive test for occult disease. Diagnostic imaging work-up includes ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), bone scintigraphy, as the more frequent sites of recurrence or metastases are cervical and mediastinal lymph nodes, lungs, liver and bone. Nuclear medicine procedures include (111)In-labelled somatostatin analogs, radioiodinated metaiodobenzylguanidine (MIBG), and several PET radiopharmaceuticals. Experience with radionuclide therapy in MTC is restricted to few patients treated with (131)I-MIBG or (90)Y-DOTATOC. Since 1987, 1 027 diagnostic MIBG scans were performed in the Department Department of Diagnostic Imaging and Therapy of the Istituto Nazionale Tumori IRCCS Foundation (Milan, Italy), 85 of which for MTC, with a sensitivity of 38.7% in patients with evidence of disease and 30.7 % if all patients were considered. Since 1994, 13 MTC patients were treated with MIBG with 4 partial responses and 4 stable diseases. Patients with liver or bone involvement responded to therapy and showed long-term partial remission of disease, others showed stability of disease, which was apparently unrelated to therapy. Improvement of efficacy can be achieved through dosimetric calculation of administered activity.