High plasma amylin/islet amyloid polypeptide levels in patients with residual medullary thyroid carcinoma after total thyroidectomy

Objective: We have previously reported that amylin/islet amyloid polypeptide (IAPP) mRNA is detected in a substantial subset of medullary carcinomas of the thyroid (MTCs). The aim of this study was to determine if the amylin/IAPP gene is expressed as the IAPP peptide in MTC tissues. Design and Methods: In 10 patients with a histological diagnosis of MTC and with persisting or recurrent disease (basal calcitonin levels .250 pg/ml), the fasting serum insulin and plasma glucose, IAPP and calcitonin levels were measured and compared with those of 18 normal control subjects matched for age and body mass index. IAPP expression was studied by immunohistochemistry in MTCs and lymph-node metastasis tissues. Results: Seven of ten MTC patients had abnormally elevated IAPP levels. Plasma IAPP and serum insulin levels were correlated in both patients and controls, but the slope of the regression line was significantly higher for MTC patients. IAPP staining was detected in four out of 12 random MTC samples and in two out of five lymph-node metastases, using immunohistochemistry. Conclusions: These results indicate that MTC cells express IAPP at the peptide level and that this raises the peripheral plasma levels. Further studies may reveal whether this is a feature of malignant disease.