Calcitonin-producing Duodenal Neuroendocrine Tumor: A Case Report and Literature Review

Introduction Neuroendocrine tumors (NETs) exhibit a wide range of clinical presentations, including the production of various hormones. Calcitonin, a sensitive marker for medullary thyroid cancer (MTC), is nonspecific and may be elevated in extra-thyroidal NETs.Case Report We present the case of a 64-year-old female patient who underwent total thyroidectomy due to a nodule in the isthmus, with a fine-needle aspiration biopsy indicating follicular neoplasia. Pathological examination revealed macro- and micro-nodular thyroid hyperplasia, along with a parathyroid adenoma. During postoperative follow-up, a progressive elevation of calcitonin was observed, reaching 64.2 pg/ml, while carcinoembryonic antigen levels remained normal. Since no MTC foci were found upon reviewing the thyroidectomy specimen, an investigation into the origin of the elevated calcitonin was initiated. Serum chromogranin A and specific neuronal enolase levels were within normal ranges. Tc-99m HYNIC-TOC scintigraphy yielded negative results. Additionally, an upper gastrointestinal endoscopy revealed a submucosal lesion in the second portion of the duodenum, with a biopsy confirming a grade 1 NET. The patient underwent Whipple surgery and hepatic metastasectomy. Postoperatively, a decrease in baseline serum calcitonin levels was observed. Seven years after surgery, she continues specialized monitoring with no biochemical or imaging evidence of disease.Conclusion Serum calcitonin contributes to the diagnosis and monitoring of anterior intestine NETs.