PRETARGETED IMMUNOSCINTIGRAPHY IN PATIENTS WITH MEDULLARY-THYROID CARCINOMA

To evaluate the use of pretargeted immunoscintigraphy (ISG) in the dia gnosis and follow-up of patients with medullary thyroid carcinoma (MTC ), we studied 25 patients with histologically proven disease; ISC was repeated after surgery in two patients. The antibody, either an antica rcinoembryonic antigen (CEA) or an antichromogranin A (CgA) biotinylat ed monoclonal antibody (MAb) or a cocktail of the two biotinylated MAb s was first injected. After 24 h, avidin was administrated i.v., follo wed by In-111-labelled biotin 24 h later. Fifty-two lesions were visua lised. Six primary rumours, diagnosed by increased calcitonin levels, were all correctly diagnosed; 47 recurrences, also suspected by blood tumour markers, were detected and confirmed by cytology or histology. In one case, single photon emission tomography allowed the detection o f small lymph nodes with a diameter of 4-7 mm. These lesions, not judg ed neoplastic by ultrasound, were confirmed to be neoplastic by fine n eedle aspiration. Pretargeted ISG correctly localises primary rumours and recurrences in MTC patients, when the only marker of relapse is se rum elevation of calcitonin. With this three-step pretargeting method, cocktails of potentially useful MAbs can be used, avoiding false-nega tive studies that may occur when CEA or CgA are not expressed.