Before you begin reading about medullary thyroid cancer, please read a description of the thyroid gland for a basic understanding of its structure and function.
Medullary thyroid cancer (MTC) is a form of thyroid cancer that originates from the parafollicular cells of the thyroid gland. The parafollicular cells secrete the hormone calcitonin. The calcitonin hormone works together with the parathyroid hormone (a protein hormone secreted by parathyroid cells) to regulate calcium levels in the body.
MTC is caused by a change or alteration in a specific gene called RET. The abnormal gene, called the RET proto-oncogene, allows affected cells to grow and multiply rapidly and function without any control or regulation. The abnormal RET gene may occur spontaneously (called a de novo mutation) or, more commonly, is passed from one generation to the next. With rare exception, if MTC is diagnosed in children, it is associated with a multiple genetic cancer syndrome called multiple endocrine neoplasia type 2 (MEN2).
People with multiple endocrine neoplasia (MEN) develop tumors in other endocrine tissues in addition to the thyroid gland. MEN is designated as MEN1 or MEN 2A or 2B based on the specific mutation and which tissues are most frequently affected. MEN1 is not associated with any form of thyroid cancer.
For patients with a mutation that leads to MEN 2A and 2B, there is a 100 percent chance of developing MTC. In MEN2, the RET gene is altered so that the protein that is produced is always “switched on.” When the RET protein is always active, cells receive signals to continuously multiply, which can contribute to cancer development. The timing of when the MTC develops can be estimated by the specific RET mutation and family history.
For patients with a RET proto-oncogene mutation, there is a 100 percent risk of developing MTC.
The symptoms associated with MTC are similar to other forms of thyroid cancer. They include a visible lump (nodule), the sensation of a lump with swallowing, hoarseness or enlarged lymph nodes that do not go away.
There are additional physical features that are associated with patients who have MEN 2B, most notable: an elongated face, nodules on the lips, tongue or on the inside cheeks of the mouth (mucosal neuromas), enlarged or swollen appearing eyelids or lips, constipation, and scoliosis.
Since MTC originates from the parafollicular cells of the thyroid gland, and parafollicular cells do not have the ability to absorb iodine, radioactive iodine (RAI) therapy is not an effective treatment as it cannot be used to treat tumor cells that have spread outside of the thyroid gland. There are several other chemotherapeutic medications that are currently under investigation. However, to date, the best these medications can do is slow down tumor growth — none appears to be able to lead to a cure.
The only effective treatment for MTC is to surgically remove the thyroid gland (total thyroidectomy). In fact, for patients with an identified RET mutation, the goal is to remove the thyroid gland before MTC develops.
Patients who have had their thyroid gland removed before MTC develops have no real risk for recurrence. For patients with MTC, the chances of remission are related to how extensively the cancer has spread. Even patients with extensive spread can experience years, and at times decades, before the tumor continues to progress.