Medullary thyroid carcinoma (MTC) is the primary cancer that produces calcitonin. MTC arises from the C cells (parafollicular cells) of the thyroid gland, which are responsible for producing calcitonin. MTC is a relatively rare form of thyroid cancer, accounting for about 3-5% of all thyroid cancer cases. Elevated levels of calcitonin in the blood are a hallmark of MTC and serve as an important diagnostic marker for the disease. It's important to note that other cancers, such as neuroendocrine tumors, can also produce calcitonin, but MTC is the primary cancer associated with high calcitonin levels. Proper evaluation and diagnosis by a healthcare professional are essential for individuals with elevated calcitonin levels to determine the underlying cause and appropriate management.