Understanding Medullary Thyroid Cancer

When most people think of thyroid cancer, they picture the more common types like papillary or follicular thyroid cancer. But there’s another, less common type that behaves differently and requires a unique approach to diagnosis and treatment: medullary thyroid cancer (MTC).

What Is Medullary Thyroid Cancer?

Medullary thyroid cancer begins in the parafollicular C cells of the thyroid gland. These specialized cells produce a hormone called calcitonin, which helps regulate calcium levels in the body. Because MTC originates in a different type of cell than most thyroid cancers, it has distinct characteristics.

MTC accounts for about 3–4% of all thyroid cancers, making it much less common than papillary thyroid cancer (the most frequent type). It can occur sporadically (with no family history) or as part of inherited genetic syndromes.

How MTC Differs From Other Thyroid Cancers

1. Cell of Origin

• Papillary and follicular thyroid cancers start in the follicular cells, which produce thyroid hormone. Papillary and follicular thyroid cancers are called differentiated thyroid cancers. “Differentiated” means the cancer cells still act a lot like normal thyroid cells: they make thyroid hormones and can take up iodine.

• Medullary thyroid cancer starts in the C cells, which produce calcitonin, a hormone that helps regulate calcium levels in the blood. C cells play a key role in maintaining calcium balance, which is vital for healthy bones, muscle function, and nerve signaling.

2. Genetic Links

• Most differentiated thyroid cancers (papillary and follicular) occur sporadically and are not caused by inherited genetic mutations. Only a very small fraction of these cancers have a familial link.

• MTC, however, can be linked to genetic mutations — most notably in the RET gene. Inherited cases are often associated with multiple endocrine neoplasia type 2 (MEN2) syndromes. This is why genetic testing and family screening are important for MTC patients.

3. Markers and Diagnosis

• Doctors typically track thyroglobulin levels in the blood as the marker for papillary or follicular thyroid cancers.

• For MTC, doctors monitor two key blood markers:

  • Calcitonin – this peptide hormone is made by C cells and is usually elevated in MTC patients.

  • Carcinoembryonic antigen (CEA) – This is another protein that is frequently elevated in MTC patients. Used as a cancer marker with calcitonin, it provides complementary information about disease activity, especially in advanced cases.

  • Both markers are used for diagnosis, prognosis, and ongoing surveillance.

4. Spread and Behavior

• Papillary thyroid cancer usually grows slowly and often spreads to lymph nodes in the neck.

• Follicular thyroid cancer can spread to blood vessels and distant organs like the lungs or bones.

• Medullary thyroid cancer can spread early to lymph nodes and distant sites, and it often behaves more aggressively than papillary or follicular types.

  MTC begins in the C can infiltrate surrounding thyroid tissue and small lymphatic channels even before a tumor is large enough to be felt. Cancer cells may also enter the bloodstream, which allows the disease to metastasize to distant organs such as the liver, lungs, or bones. This microscopic spread is one reason why thorough surgery and careful monitoring of blood markers like calcitonin and CEA are so important.

5. Treatment Approaches

• Papillary and follicular cancers: Surgery is usually followed by radioactive iodine therapy, since these cancers absorb iodine.

• MTC:

  • Radioactive iodine is not effective, because C cells do not take up iodine.

  • Traditional chemotherapy has not been shown to work well against MTC.

  • Surgery is the mainstay of treatment, often including thyroidectomy and lymph node removal.

  • For advanced or progressive disease, targeted therapies, such as tyrosine kinase inhibitors, may be used, as they are more effective against MTC than chemotherapy.

Signs and Symptoms

Like other thyroid cancers, MTC may first present as a lump in the neck. Other possible signs include:

• Swelling in the neck or lymph nodes

• Hoarseness or voice changes

• Difficulty swallowing

• Persistent cough not due to a cold

In advanced cases, symptoms related to high calcitonin or other hormones produced by the tumor may occur.

The Takeaway

Medullary thyroid cancer is rare but important to understand because it develops differently and requires specialized management compared to the more common thyroid cancers. Awareness of its unique features—especially its genetic links, blood markers, and relationship to certain medications—can lead to earlier diagnosis, better treatment planning, and improved outcomes.