Use of somatostatin analogue scintigraphy in the localization of recurrentmedullary thyroid carcinoma

Detection of recurrence of medullary thyroid carcinoma (MTC) remains a diag nostic problem. Increased serum tumour marker levels frequently indicate re currence while conventional imaging techniques (CIT) are non-diagnostic. In this study, we performed indium-111 octreotide scintigraphy and CIT in a s eries of 20 patients with MTC presenting with elevated serum tumour markers after surgery. In-111-octreotide whole-body studies detected 15 pathologic al uptake foci in 11 of the 20 patients studied and CIT detected 17 lesions in 11 of the 20 patients. Ten patients underwent reoperation, five of them with positive In-111-octreotide scintigraphy and CIT and two with positive isotopic exploration and negative CIT. Surgical findings demonstrated that the results of isotopic study and CIT had been false-positive for MTC in o ne case (sarcoidosis). The six patients with true-positive In-111-octreotid e studies had significantly higher basal calcitonin (CT) and carcinoembryon ic antigen (CEA) levels than the patients with negative isotopic studies. T he expression of somatostatin receptor (SSTR) subtypes by PC-PCR could be i nvestigated in four cases with a positive isotopic study. Among the three c ases with a true-positive study, SSTR2, the SSTR subtype that preferentiall y binds to the somatostatin analogue octreotide, was detected in two, SSTR5 was demonstrated in the three, and SSTR3 was detected in one. No subtype o f SSTR was detected in the case with a final diagnosis of sarcoidosis. We c onclude that In-111-octreotide has limited sensitivity in detecting recurre nce in patients with MTC, although its sensitivity may improve with high se rum CT levels. This radionuclide imaging technique should be employed when conventional imaging techniques ate negative or inconclusive or when the pr esence of somatostatin receptors may provide the basis for treatment with s omatostatin analogues.