A 62-year-old man, without any significant medical history, presented to a gastroenterologist with chronic diarrhea of 1-year duration. He did not take any medications except for occasional anti-inflammatory drugs. In general, he felt well. The diarrhea was sometimes associated with hematochezia. The patient’s physical examination was normal. The endoscopic work-up (upper endoscopy and colonoscopy) and abdominal ultrasound (US) were normal. Laboratory testing revealed a serum calcitonin (Ct) level of 1000 pg/mL and CEA level was 86.7 ng/mL. Thyroid and neck US showed a posterior right 13 × 10 × 10 mm hypoechoic, irregular thyroid nodule. Furthermore, a right jugular (8 × 3 mm) and a left subclavicular lymph node (47 × 19 mm) were identified. Chest and abdominal computed tomography (CT) scans showed another left jugular lymph node (23 × 20 mm), small mediastinal lymph nodes, and two left adrenal nodules (12 and 18 mm). These findings were highly suggestive of the diagnosis of medullary thyroid carcinoma (MTC). Biologic measurements excluded associated pheochromocytoma and primary hyperparathyroidism (PHPT).

Total thyroidectomy with bilateral central and jugular lymph node dissection was performed. Histological examination confirmed the diagnosis of MTC on the right (primary tumor: 2 cm in diameter), with mild C-cell hyperplasia in the left thyroid lobe and major lymph node invasion (36 out of 52 bilateral lymph nodes were involved: 15 involved nodes out 21 in the central compartment, 17/23 in ipsilateral lateral compartments, and 4/8 in the contralateral lateral compartment). The primary tumor had minimal extrathyroid extension (pT3) and the resection margins were positive (R1). Tumor was finally classified pT3 N1b Mx R1. The postoperative serum Ct level was 71 pg/mL.

MTC accounts for 5–10 % of thyroid cancers. It is histologically defined as a tumor arising from the calcitonin-secreting parafollicular C cells of the thyroid gland. MTC is known as an indolent disease despite early lymph node and distant metastatic spread. Cervical lymph node metastases are identified in 25–82 % of MTC cases [1–3]. Distant metastases at presentation are found in 7–23 % of patients [4–8]. The main distant metastatic sites are the bone, liver, and lung [9]. In general, when MTC has spread out of the neck, there are no established therapies that can offer the possibility of a cure, and the 10-year survival rate drops below 40 % [10].