Medullary thyroid cancer (MTC) is a tumor that emerges from the parafollicular cells, also called C cells, of the thyroid gland. Your thyroid is a small, butterfly-shaped gland located in the front of your neck, just below the Adam’s apple, and is responsible for sending out hormones to the rest of your body. Inside the thyroid is the medulla, which contains special cells called parafollicular C cells that produce and release hormones.
MTC happens when the C cells become cancerous and grow out of control. Medullary thyroid cancer produces calcitonin, and elevated calcitonin level is an essential feature of this tumor.