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Medullary thyroid carcinoma (MTC)

The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 21, 2021.

Medullary thyroid carcinoma (MTC) is a rare cancer that develops inside the thyroid. The thyroid is a gland that wraps around the throat just under the voice box.

Glands are a special type of organ whose purpose is to create hormones, which are chemicals that the body uses to send signals to other organs and orchestrate its regular functions.

The thyroid hormones determine your metabolism and body temperature, and when you’re young, they influence growth and development. One of these hormones, calcitonin, regulates how much calcium is in the blood and is created by special parafollicular C cells.

MTC happens when an abnormal, cancerous growth develops due to changes in these C cells in the thyroid. Cancers develop when cells undergo changes that let them grow out of control. MTC is one of the less common types of thyroid cancer, accounting for about 3 percent to 4 percent of cases (about 1,000 patients are diagnosed with it every year in the United States), according to the National Cancer Institute (NCI). It may occur in both adults and children.

Symptoms of medullary thyroid carcinoma

Many people have MTC for a long time before developing symptoms. Some of the symptoms are pretty common, which means patients frequently brush them off as no big deal.

Symptoms of medullary thyroid carcinoma include:

  • Difficulty breathing or swallowing
  • Hoarse voice
  • Lump or swelling of the throat
  • Cough that may be bloody
  • Diarrhea

What causes medullary thyroid carcinoma?

There are two main ways that MTC develops.

About 20 percent of patients develop an MTC because they have an abnormal gene they inherited, according to the American Cancer Society (ACS). When this happens, it’s called familial medullary thyroid carcinoma (FMTC).

When patients have FMTC as well as tumors that develop on additional endocrine glands, it forms a condition known as multiple endocrine neoplasia type 2 (MEN2). MEN2 increases the risk of MTC and of a rare type of tumor of the adrenal glands called pheochromocytoma.

There are two different types of MEN2:

  • MEN2A
  • MEN2B (also known as Wagenmann–Froboese syndrome and MEN3)

Patients with MEN2 usually develop MTC throughout both lobes of the thyroid gland. These patients also usually develop MTC at a younger age—as children or young adults—and the tumors spread earlier and quicker and are more aggressive.

According to the NCI, patients with MEN2A have a 90 percent chance of having an MTC and a 30 percent to 50 percent chance of getting pheochromocytoma. Those with MEN2B will develop MTC at an early age and have about a 50 percent chance of developing pheochromocytoma.

Both types of MEN2 are caused by changes in the genetic code. The body’s genetic code carries the instructions that our cells use to create proteins that perform their actions and build their structures. Sometimes there are “typos” in these instructions that break the proteins they code for.

The MEN2 syndromes are caused by typos in a gene called RET. This gene provides instructions for a protein that sends signals inside cells, playing an essential role in the growth and development of nerve cells. When this gene is broken, it keeps sending out this signal, even when it’s not needed, leading to the cells growing out of control.

Since this genetic mutation is in all of the cells, the broken RET gene may be passed from a parent with MEN2 to a child. If you have this genetic break, your doctor may suggest doing a preventive thyroidectomy to remove the thyroid before it becomes cancerous.

Finally, about 80 percent of MTC cases are not linked to MEN2, according to the ACS. These usually crop up in older adults and only in one lobe of the thyroid gland. It’s not known what causes these cases of MTC, but about 10 percent of them are due to sporadic (meaning not inherited) breaks in the RET gene in the thyroid cells, turning them into MTC, according to the ACS.

Medullary thyroid carcinoma risk factors

Although the causes of most MTC cases are unknown, there are a few factors that seem to increase the risk of developing this cancer.

  • Broken RET gene: Having a break in the RET gene that leads to MEN2 disease greatly increases your risk of developing an MTC.
  • Sporadic MTC: This isn’t linked to MEN2 disease and involves one lobe.
  • Family history: Having relatives with an MTC and related endocrine disorders or tumors may increase your risk of developing an MTC.

Having family members diagnosed with any of the following may mean you’re at increased risk of an MTC:

  • Medullary thyroid carcinoma
  • Pheochromocytoma
  • Mucosal neuromas (benign tumors of the nerve tissue), which may develop in the tongue, lips or gastrointestinal tract
  • Hyperparathyroidism, in which the parathyroid gland makes too much parathyroid hormone
  • Pancreatic neuroendocrine tumors, which develop in the hormone-producing cells of the pancreas

How medullary thyroid carcinoma is diagnosed

An MTC is usually suspected first by you or your doctor noticing a lump on your throat. Your doctor may send you for imaging tests to get a better look at what it may be.

These tests may include:

Your doctor may also send you for blood testing to determine how much of specific proteins called tumor markers are present in your blood. These tumor markers are proteins that doctors know are often produced by cancerous MTC cells. These markers include a protein called CEA and the calcitonin hormone produced by the C cells.

Along with or after imaging, your doctor may want to get a sample of the abnormal thyroid tissue. This sample is called a biopsy and is usually retrieved using a needle and local anesthesia to numb the skin. A special doctor called a pathologist will examine the sample under a microscope to determine whether the growth is cancerous and what type of cancer it may be.

If MEN2 is suspected, your doctor may screen you for broken RET genes through genetic testing. Other endocrine glands may also be checked to ensure other MEN2-related tumors aren't growing.

Creating a treatment plan

If you know you’re at risk of developing MTC due to MEN2, speak with your doctor about early screening for tumors (including blood tests and imaging tests) and potential preventive removal of the thyroid gland.

First-line treatment for MTC is the removal of the thyroid gland. Your care team will also likely take out nearby lymph nodes, small bits of white blood cell tissue that are scattered throughout the body. The lymph nodes act as transportation hubs within the body and are often the first place cancer spreads.

With the thyroid removed, you’ll need to take medications to make up for the missing hormone. If the tumor is localized to just the thyroid (stage 1 or 2 cancers), treatment may be limited to the surgical removal of the gland.

Before surgery, your care team usually tests your blood or urine for signs of pheochromocytoma. These tumors may affect your levels of epinephrine (adrenaline) and norepinephrine, which may cause problems during anesthesia.

Depending on whether the cancer is advanced, and if there are indications that it’s spread, you ay need additional treatments. Radiation therapy and chemotherapy may be recommended, but they don’t typically work very well against MTCs, which are hard to treat.

Targeted therapies and new therapies being developed through clinical trials may hold some promise to treat advanced or recurrent MTCs. You may need additional surgeries to remove tumors in other glands or if the MTC has spread to other areas of your body, such as the lymph nodes, lungs or liver.

After treatment, your doctor will want to regularly check your blood for tumor markers and thyroid hormones, which may signal that the cancer is still growing somewhere in your body.

Survival rates

Overall, 89 percent of patients diagnosed with an MTC live at least five years, according to data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program database. Other relevant rates:

  • When there are no signs that the cancer has spread beyond the thyroid, the five-year survival rate is almost 100 percent.
  • If the cancer has spread to nearby structures around the thyroid, such as the lymph nodes, the five-year survival rate is 91 percent.
  • If the cancer has spread farther, like to the bones, the survival rate is 38 percent.

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