Abstract

ABSTRACT Introduction Neuroendocrine tumors (NETs) of the thyroid are rare tumors. Medullary thyroid carcinoma (MTC) is an exact NET of the thyroid gland, arising from the parafollicular cells (C cells). It has unique features like immunohistochemically and biochemically calcitonin positivity and amyloid deposits. In this case report, a rare thyroid tumor is presented, which has neuroendocrine staining properties and does not produce serum or cytoplasmic calcitonin. Case report The patient was a 45-year-old woman who underwent total thyroidectomy because of the countless multiple thyroid nodules and a suspicion about a nodule at the right lobe. On histopathological examination, there was a tumor in the left thyroid lobe that measured 0.4 cm. Tumor immunohistochemical staining was positive for synaptophysin, chromogranin A (neuroendocrine cell markers), and thyroglobulin (Tg), and thyroid transcription factor-1 (TTF-1; follicular cell markers). The staining was negative for calcitonin. Conclusion There are thyroid tumors that are calcitonin-negative and Tg-positive called calcitonin-negative NETs. Careful interpretation and distinction between MTCs are needed at these tumors because they may have different biologic behaviors, and calcitonin negativity makes follow-up of patients challenging. How to cite this article Özden S, Colak A, Saylam B, Cengiz Ö. Primary Calcitonin-negative Neuroendocrine Tumor. World J Endoc Surg 2017;9(3):104-108.

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