What is medullary thyroid carcinoma (MTC)?

Updated: May 14, 2020
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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MTCs represent approximately 5% of all thyroid malignancies. A slight female preponderance is observed. Tumors arise from the parafollicular C cells of the thyroid gland. C cells are neural-crest derivatives and produce calcitonin. About 75% of MTCs occur sporadically, and 25% occur familially. Familial cases are commonly multifocal throughout the thyroid gland, whereas sporadic cases are usually not multifocal.

Patients may present with clinical evidence of MTC, or they may present before MTCs develop if they are from a family with known FMTC syndrome. New germline mutations can also occur. Patients with new germline mutations present with MTCs without a positive family history, but they are at risk for passing on the syndrome.

The FMTC syndromes consist of MEN 2A, MEN 2B, and FMTC. They are inherited in an autosomal dominant fashion. Children inheriting an FMTC syndrome have a 100% risk of developing MTC.

MEN 2A (Sipple syndrome) consists of MTC, pheochromocytoma (in 50% of patients), and hyperparathyroidism (10-20% of patients). MEN 2B consists of MTC, pheochromocytoma (in 50% of patients), marfanoid habitus, and ganglioneuromatosis. FMTC consists of MTC alone. MTC in MEN 2B has the most aggressive biologic features. In this situation, MTC usually develops by the age of 10 years, and it has a high propensity for rapid growth and metastasis. MTC in MEN 2A can appear in the first decade of life, and it almost always develops by the second decade. MTC in FMTC usually develops during adulthood.

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