Endocrine Abstracts

Introduction: Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor (1-2% of all thyroid carcinomas), which arises from calcitonin-producing C cells. Calcitonin (CT) and carcinoembryonic antigen (CEA) are used as tumor markers in the follow-up of patients with MTC. Non-secretory forms of MTC are very rare, accounting for less than 1% of the cases.

Case Report: A 53-year-old man underwent left thyroid lobectomy for a 1.1 cm thyroid nodule subjected to fine-needle aspiration twice, which cytology revealed a “follicular lesion of undetermined significance. Histological examination showed a multifocal MTC (1.2 cm and 0.4 cm) and C-cell hyperplasia. Immunohistochemistry revealed cytoplasmic positivity for CT, chromogranin and synaptophysin, and nuclear positivity for TTF1. Totalization of thyroidectomy and lymph node dissection of the central compartment were performed. Histopathological analysis revealed C-cell hyperplasia and absence of lymph node metastasis in 26 lymph nodes. Preoperatively, there was no elevation of CT or CEA [CT 2.84 pg/ml (NR: 0.40-18.90) and CEA 2.4 ng/ml (NR: <5.0)]. A dilution test for CT was performed and showed no evidence of interference caused by heterophile antibodies. The measurement of fractionated 24-h urinary metanephrines and phospho-calcium metabolism did not show any changes. The search for mutations in the RET gene was negative. In the postoperative study, CT and CEA measurements remained within the normal range. 18F-DOPA positron emission tomography (PET) was requested, which revealed a moderate uptake located in the topography of the duodenal arch. The patient was referred to the Gastroenterology outpatient clinic. He underwent endoscopic ultrasound and abdominal computerized-tomography scan. No duodenal or locoregional lesions were observed. The patient is currently under surveillance, with no clinical, analytical or imaging evidence of recurrent disease.

Conclusion: The reported cases of non-secretory MTC are rare and present a heterogeneous clinical course, which makes it difficult to predict its behavior. It is not clear what is the best way to monitor these patients, as the use of tumor markers is limited. Alternative methods for monitoring are needed to optimize the follow-up of these patients.