Is there an ectopic secretion of monomeric calcitonin in the human being?

Introduction: Persistent detectable calcitonin (CT) values can be frequently observed after treatment of medullary thyroid carcinomas (MTCs). Apart from residual C cells or incomplete tumor extirpation, ectopic CT production should be taken into account. CT determination in patients without MTC and after total thyroidectomy should reveal to what extent, apart from the C cells, other neuroendocrine cells show a relevant CT production. Objectives: The objective of this study was to find out whether ectopic CT production can be detected using an assay specifically recognizing the monomeric form of CT. Methods: The CT serum values were obtained from 94 healthy individuals and 64 patients who had undergone total thyroidectomy and radioiodine therapy because of follicular or papillary carcinoma. Results: In the group of thyroidectomized patients, the CT values were below the detection limit of the assay. In the tested patients, there was neither a physiological (C cell) nor a pathological (MTC cell) secretion of monomeric CT. Conclusion: A relevant ectopic monomeric CT production could be excluded because the patients were without detectable CT concentration. For this reason, postoperative CT concentrations of the monomeric form in MTC patients can be traced either to remaining C cells or to tumor cells. For a differentiation of these two possibilities further diagnostics is necessary.