Medullary thyroid cancer (MTC) is a rare type of cancer that forms in the thyroid. It differs from other forms of thyroid cancer, as it originates in different cells, known as parafollicular C cells.

The thyroid is a small gland present in the front of the neck, which plays an important role in producing hormones that regulate the body. Thyroid cancer occurs when atypical cells in the thyroid begin to grow uncontrollably. According to the American Cancer Society (ACS), types of thyroid cancer vary depending on the cells in which the cancer develops.

Evidence suggests MTC is the rarest type of thyroid cancer, accounting for 3–4% of all thyroid cancers and affecting about 1,000 people in the United States each year.

In this article, we will provide an overview of medullary thyroid cancer, including symptoms, treatment, and outlook.

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The thyroid gland is a butterfly-shaped gland in the front of the neck that produces thyroid hormones, which help regulate the body’s metabolic rate. The thyroid gland contains two main types of cells: follicular cells and C cells, which are also known as parafollicular cells.

Follicular cells are responsible for producing the thyroid hormones, while parafollicular cells produce the hormone calcitonin. This hormone helps control how the body uses calcium. MTC differs from other types of thyroid cancer, as it develops in parafollicular cells. Some people may also refer to MTC as medullary thyroid carcinoma.

There are two types of MTC: sporadic and familial. Sporadic is the more common type, typically occurring in older adults and only affecting one thyroid lobe. Familial MTC runs in families and usually develops during childhood or early adulthood. People with this type may have cancer in both thyroid lobes and may also have a higher risk of other kinds of tumors.

The name refers to the location of the parafollicular C cells, which are present in the medulla of the thyroid. MTC is also often more difficult to find and treat than other thyroid cancers.

MTC tends to develop slowly. As such, a person may not have any symptoms during the early stages of the condition. When symptoms do develop, they usually present as a lump or nodule in the neck, corresponding with the mass of cells growing in the thyroid. If the nodule is large enough, it may also cause breathing or swallowing difficulties and a hoarse voice.

Less common symptoms may include:

  • a red face, or flushing
  • weight loss
  • loose stools, or diarrhea

As with many cancers, doctors stage MTC with four stages running from 1 to 4. Classifying the stage of cancer depends on different factors, such as the size of the tumor and whether it has spread to lymph nodes or distant organs.

While age is a factor for staging other types of thyroid cancer, it does not play a role in MTC staging.

Stage 1 is the earliest stage when the tumor is smallest and has not yet spread. Severity increases with each stage until stage 4, at which point the cancer can be any size and may have grown and spread to nearby structures and distant sites.

MTC is the result of alterations in parafollicular cells. However, as most cases are sporadic, the exact cause is unknown.

For the 25% of MTC cases that run in families, evidence notes these individuals carry a change in the RET gene. This gene is present on chromosome 10 and plays a role in cell signaling. Scientists have associated changes in this gene with several sporadic cancers, such as MTC.

The changes in the RET gene cause a condition known as multiple endocrine neoplasia type 2, or MEN2. Evidence indicates that there are two types of MEN2: MEN2A and MEN2B.

Usually, people with MTC will present with a lump in their neck. Initial diagnosis will typically begin with a doctor checking this lump. They may then use imaging tests, such as ultrasound, CT, or MRI, to scan the thyroid.

If a doctor suspects thyroid cancer, they will likely perform a fine needle aspiration biopsy of the nodule. This involves taking a small amount of tissue from the nodule using a very thin needle. A pathologist will then look at the sample and see if cancer cells are present.

A doctor may also want to perform further tests to confirm the diagnosis and provide more information to help with treatment plans. This may include blood tests to check levels of calcitonin, calcium, and carcinoembryonic antigen (CEA).

The primary treatment for MTC is surgery, known as a thyroidectomy. It involves the total removal of the thyroid gland and will require a person to take thyroid hormone replacement medication for life.

In addition to surgery, people may also require other types of treatment, particularly if the tumor has spread to sites outside the thyroid or outside the neck. These treatments may also be an option if a person is not suitable for surgery. These options may include:

  • external beam radiation
  • chemotherapy
  • targeted therapies

The best management approach depends on the stage of cancer at diagnosis. If cancer has spread, treatment often involves an aggressive approach with multiple strategies and a combination of chemotherapy medications.

According to the ACS, most forms of thyroid cancer are not preventable, as they typically occur sporadically.

However, if an individual knows they have a family history of MTC, they may wish to test for certain gene changes that may indicate a risk of this disease. If a person has a high risk, a doctor may perform a thyroidectomy to prevent cancer from developing.

Evidence notes that MTC may reoccur even years after an initial diagnosis. Usually, routine monitoring and follow-up checks continue for years after a diagnosis.

Many tests are available that may identify recurrent or metastatic disease. Part of the follow-up checks will likely include blood tests that measure calcitonin levels. After surgery to remove the thyroid, calcitonin levels are typically undetectable. If levels rise, it could indicate a reoccurrence.

The outlook or prognosis for people with MTC varies. Factors, such as staging at diagnosis, response to treatment, and overall health, play a role in recovery and prognosis.

While the prognosis of MTC is not typically as favorable as other thyroid cancers, early detection and treatment can yield optimal outcomes. Additionally, routine monitoring of biomarkers, such as calcitonin or CEA, over the first year after surgery can be a useful predictor for survival rates.

MTC occurs less often than other forms of thyroid cancer, so data on survival rates may not be completely accurate. Although there is currently no cure, people can live with MTC for many years, and research continues on treatment options that may improve survival rates. According to 2017 research, the 10-year MTC survival rates are:

  • 95% with localized cancer only in the thyroid gland
  • 75% with regional disease without spread to distant organs
  • 20% with distant spread to organs, such as the liver or lungs

If a person experiences a lump on their neck with no known cause, they should contact a doctor. People should also be aware of potential symptoms of MTC, such as difficulty breathing or swallowing.

Additionally, if individuals have a known family history of MTC, they should consider consulting a healthcare professional. A doctor may recommend genetic tests to determine if they have the gene changes that may result in MTC.

MTC is a rare form of thyroid cancer that develops in the parafollicular C cells. While early stage MTC may not cause any symptoms, a person may notice a lump in the neck near the thyroid gland. Researchers are not sure of the exact cause of the disease, as many cases occur sporadically. However, roughly a quarter of MTC cases have a genetic link.

Treatment options typically include surgery to remove the thyroid. Additional treatments may include chemotherapy, radiation, and targeted therapies. Prognosis largely depends on the stage of disease at diagnosis and how people respond to treatment.