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Medullary thyroid carcinoma (MTC) arises from the parafollicular cells (C cells) of the thyroid gland that produce the hormone calcitonin that regulates blood calcium levels. Most cases (80%) of MTC are sporadic, meaning that the disease does not run in families. A second type of MTC, known as familial MTC, is an inherited form of thyroid cancer that tends to run in families and accounts for about 20% of all cases of MTC. Patients with familial MTC can also develop tumors of other endocrine organs - a syndrome known as type 2 multiple endocrine neoplasia (MEN-2). Two types of MEN-2 have been identified:

• MEN-2A - In patients with MEN-2A, MTC occurs in conjunction with tumors of the adrenal glands called pheochromocytomas and tumors of the parathyroid glands that cause hyperparathyroidism (a condition in which the body produces excessive amounts of parathyroid hormones disrupting the regulation of calcium in the body).

• MEN-2B - In patients with MEN-2B, MTC occurs in conjunction with adrenal gland tumors (pheochromocytoma) but without tumors of the parathyroid glands.

Typically, patients with MTC present with a thyroid nodule and cervical lymphadenopathy (enlargement of the lymph nodes in the neck). They may also have additional symptoms of MEN-2 including diarrhea, pheochromocytoma, and hypercalcemia (elevated blood levels of calcium).

The standard treatment for patients with MTC, for both the sporadic and familial forms of the disease, is total thyroidectomy. Central neck compartment dissection (surgical removal of lymph nodes next to the thyroid gland) and bilateral lymph node dissection (surgical removal of regional lymph nodes on both sides of the neck) are also usually performed due to the high incidence of lymph node involvement in patients with MTC.

Unlike differentiated thyroid cancer, MTC is not sensitive to radioactive iodine therapy and this treatment is not used for the management of patients with MTC. Some patients with MTC may also require external-beam radiation therapy after surgery to remove the thyroid gland and regional lymph nodes. Radiation therapy may be considered in patients with:

• Locally advanced MTC at the time of diagnosis
• Persistently high blood levels of calcitonin after surgery
• Bulky tumors that cannot be removed by surgery

As is the case with differentiated thyroid carcinoma, patients with MTC also require thyroid hormone replacement pills for the rest of their lives since they can no longer produce these essential hormones naturally. Patients with MTC should also be tested for other endocrine tumors (pheochromocytoma and parathyroid gland tumors) that are associated with MEN-2 syndrome. Treatment with drugs known as somatostatin analogues can help to control symptoms of MEN-2 such as diarrhea. After surgery, patients with MTC should be monitored for serum levels of calcitonin and carcinoembryonic (CEA) antigen. Abnormal levels of these two tumor markers are suggestive of residual disease or distant metastases. If serum levels of these tumor markers are elevated, additional follow-up diagnostic imaging studies including ultrasonography of the neck, CT scan of the chest, and MRI of the liver are usually required to detect either residual tumor or distant metastases.