Conditions and symptoms
What Is Medullary Thyroid Carcinoma? GLP-1 Warning
Medullary thyroid carcinoma · say it: MED-yoo-lair-ee THY-royd kar-sih-NOH-muhAlso written: MTC, medullary thyroid cancer
Short answer
Medullary thyroid carcinoma is a rare type of thyroid cancer that starts in the thyroid's C-cells, which make the hormone calcitonin.
What it means
Medullary thyroid carcinoma (MTC) is an uncommon thyroid cancer. It starts in C-cells, which make calcitonin, rather than in the cells that make thyroid hormone. Some cases are inherited, as part of conditions called Multiple Endocrine Neoplasia type 2 (MEN 2), which is why family history matters. A lump in the neck, hoarseness or trouble swallowing should be checked by a doctor.
It appears on the labels of GLP-1 receptor agonists (such as semaglutide, liraglutide and dulaglutide) and related medicines. Their boxed warning says they caused C-cell tumours in rodents, and that it is unknown whether they do in humans. The medicines should not be used by people who have had MTC or have a family history of MTC or MEN 2. Labels ask you to report a neck lump, hoarseness or trouble swallowing.
It differs from the more common papillary and follicular thyroid cancers, and from benign thyroid nodules.
Where you may see it
- Boxed warnings on GLP-1 receptor agonist labels
- Thyroid ultrasound and biopsy reports
- Endocrinology and genetics clinic letters
📄 How it looks on a report
Counsel patients regarding the potential risk of MTC and symptoms of thyroid tumors (e.g., a mass in the neck, dysphagia, dyspnea, persistent hoarseness).
🙅 What it does not mean
- The label warning does not mean the medicine is known to cause this cancer in people.
- Most thyroid lumps are not medullary thyroid carcinoma.
- It is not the same as the more common types of thyroid cancer.
🗒️ Questions to ask your doctor
💊 Medicines whose labels mention “Medullary thyroid carcinoma”
Plain-English explanations of each medicine, from its official FDA label.
- Liraglutide
a GLP-1 receptor agonist, a type of medicine that acts like a natural gut hormone called GLP-1 to help lower blood sugar
- Semaglutide
A GLP-1 receptor agonist, a type of medicine that works like the natural GLP-1 hormone in the body
🔗 Read more from trusted sources
- “Medullary thyroid carcinoma” on MedlinePlus ↗
US National Library of Medicine
- NCI Dictionary definition ↗
US National Cancer Institute: “medullary thyroid cancer”
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