Metastatic Medullary Thyroid Carcinoma with Normal Serum Calcitonin Levels

ABSTRACT Objective: Medullary thyroid carcinomas (MTCs) originate from parafollicular C cells and produce the hormone calcitonin, which is primarily responsible for the biochemical dysfunction in calcium metabolism seen in MTC. MTCs constitute only about 5 to 7% of thyroid neoplasms. In rare cases, serum calcitonin can be normal or undetectable. Methods: We present the clinical examination and laboratory findings of a patient with MTC and a review of the literature. Results: A female of 65 years was suspected to have MTC after fine-needle aspiration cytology but serum calcitonin was normal. A total thyroidectomy was performed. Histopathology confirmed MTC. During the 9-year follow-up period, she had persistently normal serum calcitonin level despite lymph node metastasis. Conclusion: Raised serum calcitonin is a biochemical hallmark of diagnosis and recurrence of MTC in the post-surgical period. Our patient, however, is a case of MTC with postsurgical recurrence and metastasis but persistently normal calcitonin. Such cases are challenging in management. We have not found another report in the literature with the combination of normal calcitonin, MTC, and postsurgical recurrence with metastasis in lymph nodes. Abbreviations: CEA = carcinoembryonic antigen; CT = calcitonin; CT-NEG-MTC = calcitonin-negative medullary thyroid cancer; FNAC = fine-needle aspiration cytology; MTC = medullary thyroid carcinoma