Parafollicular C cells
MTC begins in the C cells of the thyroid, not the main follicular cells. These C cells make calcitonin, which becomes a built-in marker for the disease.
A rarer, calcitonin-producing thyroid cancer
Medullary thyroid cancer — (MTC) explained
Medically reviewed by Dr. Owais Mohammed, Medical Oncologist, MBBS · MD · Last reviewed June 2026
Medullary thyroid cancer (MTC) is an uncommon thyroid cancer that starts in the thyroid's C cells — the cells that make a hormone called calcitonin. It behaves differently from the more common thyroid cancers, and about one in four cases is linked to an inherited change in the RET gene. Understanding it helps you ask the right questions and get the right care.
- A calcitonin cancer — MTC cells make calcitonin, a marker used to diagnose and follow it
- The RET gene matters — about a quarter of cases are hereditary and worth testing
- Surgery is the main treatment — radioactive iodine does not work for MTC
- Family can be checked too — RET testing protects your relatives, not just you
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What Is Medullary Thyroid Cancer (MTC)?
The thyroid is a small, butterfly-shaped gland at the base of the neck. Most thyroid cancers begin in its main, hormone-making follicular cells. Medullary thyroid cancer is different — it begins in a separate group of cells called the parafollicular C cells, which produce a hormone called calcitonin.
Because of this, mtc thyroid cancer is sometimes described as a calcitonin cancer: the tumour keeps making calcitonin, and a simple blood test for that hormone becomes one of the most useful ways to diagnose it and follow it over time. MTC is uncommon, making up only about 1 to 2 in every 100 thyroid cancers.
The other important feature of MTC is its link to genetics. Around one in four cases is hereditary — caused by a change in the RET gene that can run in families. This is why MTC is handled a little differently from the more common thyroid cancers, and why testing for that gene matters so much.
Did you know?
Medullary thyroid cancer does not respond to radioactive iodine — the treatment that works so well for the more common thyroid cancers. Because MTC begins in the C cells, which do not take up iodine, surgery to remove the thyroid and neck lymph nodes is the cornerstone of treatment. (Source: NCCN Clinical Practice Guidelines in Oncology — Thyroid Carcinoma.)
Why MTC is treated differently
How Medullary Thyroid Cancer Differs From Other Types
Knowing how MTC is different helps explain why the tests and treatment are not the same as for papillary or follicular thyroid cancer.
Calcitonin & CEA
A calcitonin blood test, usually with CEA, helps confirm MTC and track it after surgery. Few cancers come with such a useful marker built in.
The RET gene link
About one in four MTCs is hereditary, driven by a faulty RET gene. That is why genetic testing and family counselling are part of standard care.
Surgery, not iodine
Radioactive iodine does not work for MTC. Careful surgery to remove the thyroid and central neck nodes is the main treatment, done well the first time.
Who Is More Likely to Get Medullary Thyroid Cancer?
Most people who develop medullary thyroid cancer have no family history at all — these cases are sporadic, meaning the RET change happened by chance within the thyroid and is not inherited. Sporadic MTC tends to appear in adults in their 40s, 50s and 60s.
The hereditary form is different. It is caused by a faulty RET gene passed down through a family, often as part of an inherited condition called Multiple Endocrine Neoplasia type 2 (MEN2A or MEN2B). People with hereditary MTC may develop it younger, and may have other linked conditions such as an adrenal tumour. A family history of medullary thyroid cancer is the single biggest reason to be tested.
If you have a relative with MTC or a known RET change, a simple genetic test can tell you whether you carry the same gene — long before any cancer develops. Speak to a CION specialist about testing for you and your family.
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MTC Needs a Team That Knows It Well
Because medullary thyroid cancer behaves differently, the right first operation and the right testing matter. Our tumour board reviews every case together — no rushed decisions, no unnecessary tests.
How Medullary Thyroid Cancer Is Diagnosed
Diagnosing MTC carefully matters, because the results decide how much surgery is needed and whether your family should be tested. The steps below are usually done before any operation is planned.
Neck ultrasound and FNAC
A painless neck ultrasound looks closely at the thyroid nodule and the nearby lymph nodes. A fine needle aspiration (FNAC) then takes a small sample of the lump, so the type of cell can be examined under the microscope.
Calcitonin and CEA blood tests
A blood test for calcitonin is central to MTC — a raised level strongly suggests the disease and shows how much may be present. A second marker called CEA is usually measured alongside it. Together they also guide follow-up after treatment.
RET genetic testing
Everyone diagnosed with MTC is offered a test for changes in the RET gene. This tells you whether the cancer is the hereditary form, which has implications for your relatives, and can also guide treatment if the disease is advanced.
Checking for linked conditions and spread
Because hereditary MTC can come with other tumours, doctors may check for the conditions linked to MEN2 — such as an adrenal tumour — before surgery. Imaging like CT may be used to map how far the cancer has spread, so the right operation is planned first time.
Did you know?
A single calcitonin blood test can do something most cancers cannot — it tracks medullary thyroid cancer over time. After surgery, a falling or undetectable calcitonin level is reassuring, while a rising level can flag a return of disease early, often before any symptom appears. (Source: American Thyroid Association MTC guidelines.)
How Medullary Thyroid Cancer Is Treated
The treatment of MTC is led by surgery, and getting that first operation right gives the best chance of long-term control.
Surgery. The usual operation removes the whole thyroid (a total thyroidectomy) together with the lymph nodes in the central part of the neck, because MTC tends to spread to these nodes early. Removing affected nodes at the same time helps avoid further surgery later.
Not radioactive iodine. Unlike the common thyroid cancers, MTC does not take up iodine, so radioactive iodine therapy is not used. This is one of the most important reasons to be sure of the exact cancer type before treatment begins.
Targeted medicines for advanced disease. If MTC has spread or comes back and cannot be removed, medicines that block the RET pathway can help control it. Knowing your RET status helps doctors choose between them. External radiotherapy is occasionally used for specific situations.
Every treatment plan at CION is decided by a tumour board — medical, surgical and radiation oncologists together — not a single doctor's opinion. You can read more about the wider pathway on our thyroid cancer treatment page.
Why Patients With MTC Choose CION Cancer Clinics
Because medullary thyroid cancer is uncommon and needs a particular approach, it helps to be cared for by a team that treats it regularly. Here is what you can expect at CION.
- Free 45-minute consultation — unhurried time with a specialist to explain your diagnosis and the plan ahead
- Tumour board for every patient — your case is reviewed by surgical, medical and radiation oncologists together
- RET genetic testing and counselling — for you and, where needed, for your family
- The right first surgery — careful thyroid and neck-node surgery, planned to be done well the first time
- No unnecessary tests, ever — investigations are arranged only when they genuinely change your care
- Transparent costs and clear next steps — decisions for healing, not billing
A medullary thyroid cancer diagnosis raises a lot of questions — about you and your family. Book a free consultation and we will walk this journey with you.
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Common questions
Medullary Thyroid Cancer — Your Questions Answered
What is medullary thyroid cancer (MTC)?
Medullary thyroid cancer (MTC) is an uncommon type of thyroid cancer that makes up roughly 1 to 2 in every 100 thyroid cancers. Unlike the more common papillary and follicular types, MTC starts in the parafollicular C cells of the thyroid — the cells that produce a hormone called calcitonin. Because of this, MTC is sometimes called a calcitonin cancer, and a calcitonin blood test is a key part of diagnosis and follow-up. About one in four cases is hereditary and linked to a change in the RET gene. MTC behaves differently from other thyroid cancers, so it needs care from a team experienced in treating it.
What causes medullary thyroid cancer?
Medullary thyroid cancer is caused by changes in the RET gene that make the C cells of the thyroid grow out of control. In about three out of four people the change is sporadic — it happens by chance in the thyroid cells and is not inherited. In the remaining cases it is hereditary: a faulty RET gene is passed down through families, often as part of an inherited condition called Multiple Endocrine Neoplasia type 2 (MEN2A or MEN2B). Because the inherited form can be passed to children, anyone diagnosed with MTC is usually offered RET genetic testing and family counselling.
What is the role of calcitonin in medullary thyroid cancer?
Calcitonin is a hormone made by the C cells of the thyroid — the same cells that medullary thyroid cancer starts in. Because MTC cells continue to make calcitonin, a blood test for calcitonin is one of the most useful tools doctors have. A raised calcitonin level can point to MTC, help judge how much disease is present, and is used after surgery to check whether any cancer remains or returns. A related blood marker called CEA is often measured alongside it. These markers make MTC easier to monitor over time than many other cancers.
Is medullary thyroid cancer hereditary?
It can be. About one in four cases of medullary thyroid cancer is hereditary — caused by a faulty RET gene passed down through a family, usually as part of Multiple Endocrine Neoplasia type 2 (MEN2). The other three in four cases are sporadic and not inherited. Because the difference matters for you and your relatives, RET genetic testing is offered to everyone diagnosed with MTC. If an inherited change is found, close family members can be tested too, and those who carry the gene can be monitored or offered preventive surgery long before cancer develops.
What is the RET gene and why does it matter in MTC?
The RET gene carries the instructions for a protein that helps cells grow and signal normally. When the RET gene is faulty, the C cells of the thyroid can grow uncontrollably and form medullary thyroid cancer. RET changes can be inherited or can arise within the tumour itself. Testing for RET matters for two reasons. First, an inherited RET change has implications for your family, who can then be tested. Second, certain RET-targeted medicines are now available for advanced MTC, so knowing the RET status can guide treatment choices in disease that has spread.
What are the symptoms of medullary thyroid cancer?
The most common first sign of medullary thyroid cancer is a painless lump or swelling in the front of the neck, often with swollen lymph nodes nearby. As with other thyroid cancers, it can also cause a hoarse voice, difficulty swallowing, or neck discomfort if the lump presses on surrounding structures. Because MTC cells release hormones, advanced disease can occasionally cause persistent diarrhoea or facial flushing. Many of these signs are easy to mistake for harmless conditions, so a neck lump — especially in someone with a family history of thyroid cancer — should always be checked with an ultrasound and a calcitonin blood test.
How is medullary thyroid cancer diagnosed?
Diagnosis usually begins with a neck ultrasound to look at the thyroid nodule and nearby lymph nodes, followed by a fine needle aspiration (FNAC) to sample the lump. A calcitonin blood test is central to diagnosis, because a raised level strongly suggests medullary thyroid cancer; a CEA blood test is often done alongside it. If MTC is confirmed, doctors arrange RET genetic testing and may check for the conditions linked to MEN2, such as an adrenal tumour, before any surgery. Imaging such as CT may be used to map the extent of disease. This careful work-up ensures the right operation is planned the first time.
How is medullary thyroid cancer treated?
The main treatment for medullary thyroid cancer is surgery — usually removal of the entire thyroid (total thyroidectomy) together with the lymph nodes in the central part of the neck, because MTC tends to spread to these nodes early. Getting this first operation right is important, as it offers the best chance of long-term control. Medullary thyroid cancer does not respond to radioactive iodine, which is used for other thyroid cancers, so that treatment is not part of the plan. For disease that has spread or come back, targeted medicines that block the RET pathway can be used. Every plan at CION is decided by a tumour board, not a single doctor.
Does medullary thyroid cancer respond to radioactive iodine?
No. Radioactive iodine therapy works on the follicular cells of the thyroid, which take up iodine. Medullary thyroid cancer starts in the parafollicular C cells, which do not take up iodine, so radioactive iodine is not an effective treatment for MTC. This is one of the key ways MTC differs from the more common papillary and follicular thyroid cancers. Instead, treatment relies on careful surgery to remove the thyroid and affected lymph nodes, with targeted medicines and occasionally external radiotherapy reserved for advanced or recurrent disease. It is important your cancer type is confirmed so the right treatment path is followed.
What is the outlook for medullary thyroid cancer?
The outlook for medullary thyroid cancer depends mainly on the stage at diagnosis and how completely the cancer can be removed by surgery. When MTC is found while it is still inside the thyroid, many people do very well over the long term. When it has already spread to lymph nodes or beyond, it can be harder to control, but it often grows slowly and can be monitored using calcitonin and CEA blood markers. Because outcomes vary so much from person to person, it is best to discuss your specific situation with a thyroid cancer specialist rather than rely on general figures.
Should my family be tested if I have medullary thyroid cancer?
If RET genetic testing shows that your medullary thyroid cancer is hereditary, then yes — your close blood relatives should usually be offered testing too. Identifying family members who carry the same RET change is one of the most valuable things that can come from your diagnosis. Relatives who carry the gene can be monitored closely, and in some cases offered preventive removal of the thyroid before cancer ever develops. If your testing shows the cancer is sporadic and not inherited, family testing is not needed. At CION, genetic counselling is part of how we care for every MTC patient and their family.
Disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified oncologist for guidance specific to your situation. This page is periodically reviewed and updated by CION's medical team in line with current clinical guidelines.
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