Medullary thyroid cancer is the outlier of the thyroid cancers, and almost everything that makes it different comes down to one thing: it arises from a cell type that secretes a hormone into the blood. That single fact gives this disease something the far more common papillary and follicular cancers do not have, which is a blood test that genuinely does diagnostic work. Calcitonin identifies it, tracks it, predicts where it has spread, and forecasts how it will behave. This guide explains what medullary thyroid cancer is, how it differs from the thyroid cancers most people read about, why the laboratory markers matter so much here, how inheritance works through the RET gene, and what the treatment and survival picture looks like.
What medullary thyroid cancer is
The thyroid contains two distinct cell populations. Follicular cells make thyroid hormone and give rise to papillary and follicular cancers, which together account for the overwhelming majority of cases. Parafollicular cells, known as C cells, make a different hormone called calcitonin. Medullary thyroid carcinoma arises from those C cells.
It is uncommon. Estimates of its share range from about 2 to 10 percent of thyroid cancers depending on the series, with roughly 1,000 new diagnoses a year in the United States. Because it does not come from follicular cells, it does not absorb iodine, does not produce thyroglobulin, and does not respond to the radioactive iodine treatment that is central to managing differentiated thyroid cancer. For the wider picture of the other types, see our thyroid cancer guide.
How it differs from papillary and follicular thyroid cancer
| Feature | Papillary and follicular | Medullary |
|---|---|---|
| Cell of origin | Follicular cells | Parafollicular C cells |
| Blood marker followed | Thyroglobulin, after the gland is removed | Calcitonin and carcinoembryonic antigen |
| Takes up radioactive iodine | Yes, which makes iodine treatment possible | No |
| Inherited forms | Uncommon | Up to a quarter of cases |
| Main driver | Varied, commonly BRAF or RAS changes | RET, inherited or acquired |
The practical consequence is that treatment decisions, follow-up schedules, and even the blood tests ordered afterwards are different from the outset. Advice written about thyroid cancer in general often does not apply here.
Symptoms
The presentation is usually a lump rather than a feeling of illness. A neck nodule is present in roughly 75 to 95 percent of people at diagnosis, and enlarged lymph nodes in the neck in about 70 percent, which reflects a tendency to involve nodes earlier than papillary disease does.
- A firm lump in the front or side of the neck
- Swollen lymph nodes in the neck that do not settle
- Hoarseness or a persistent change in the voice
- Difficulty swallowing or, less often, breathing
- Diarrhoea or flushing, which are unusual but can occur when calcitonin and related peptides are very high in advanced disease
Thyroid function itself is typically normal, so a routine thyroid panel gives no warning; our TSH blood test guide explains what that panel does and does not measure, and our guide to normal thyroid levels covers the pattern as a whole. Because a nodule is the usual starting point, read our thyroid nodule blood test guide for what that first assessment involves.
Sporadic and inherited forms
About three quarters of cases are sporadic, meaning they arise in a person with no family history. The remaining quarter are inherited, caused by a germline change in the RET gene passed down in families. RET provides instructions for a protein involved in cell signalling, and certain changes make it signal continuously, driving cells to divide when they should not.
The inherited forms fall into recognised patterns. In multiple endocrine neoplasia type 2A, medullary thyroid cancer occurs alongside a risk of phaeochromocytoma, a tumour of the adrenal gland, and of overactive parathyroid glands. In type 2B, the disease tends to appear earlier and is accompanied by other physical features. Familial medullary thyroid carcinoma describes families in which this cancer is the only feature.
Because MEN2A involves the parathyroid glands, calcium is monitored in these families; consult our calcium blood test guide and, for the hormone that controls it, our PTH blood test guide.
Why genetic testing changes things
Anyone diagnosed with medullary thyroid cancer is generally offered RET testing, because a positive result has consequences that extend well beyond the individual. It identifies relatives who may carry the same change, it prompts screening for the associated adrenal and parathyroid conditions, and in some families it supports removing the thyroid before cancer develops. The specific RET change also influences how early that is considered. This is one of the clearest examples in medicine of a test result that belongs to a family rather than to one person, and it is a conversation for a specialist genetics service.
The blood tests that carry this diagnosis
In most cancers, blood markers are used for monitoring after the diagnosis has been made by imaging and biopsy. Medullary thyroid cancer is different, and this is the part worth understanding properly.
| Marker | What it is | What it is used for |
|---|---|---|
| Calcitonin | The hormone C cells produce | Detection, extent of disease, and follow-up after surgery |
| Carcinoembryonic antigen | A protein many tumours release | Second marker; its trend carries prognostic weight |
| Doubling time | How fast either marker is rising | One of the strongest available predictors of behaviour |
Calcitonin is the marker that identifies the disease, and our calcitonin blood test guide covers how a single result should be read. The essential caution is that a raised calcitonin has a long list of explanations that are not cancer, including kidney disease, proton pump inhibitors, smoking, and pregnancy, so one elevated value is a reason to repeat the test rather than a diagnosis.
Carcinoembryonic antigen, usually shortened to CEA, is measured alongside it; our CEA blood test guide explains why this marker is read as a trend rather than a snapshot. In medullary thyroid cancer that principle is formalised: after treatment, the speed at which calcitonin or CEA rises, expressed as a doubling time, is used to judge how the disease is behaving and how closely it needs watching.
How the diagnosis is made
The sequence usually begins with a thyroid nodule found on examination or on a scan. Ultrasound describes it, and a fine-needle aspiration takes cells for examination. The complication specific to this disease is that standard cytology misses a substantial share of medullary cancers, which is why measuring calcitonin in the fluid washed from the needle has become an important addition. Imaging with PET is used mainly to locate disease that has recurred rather than to make the initial diagnosis. Where calcitonin sits in an indeterminate range, a stimulation test is sometimes used in selected cases, a practice discussed in the research section below.
Treatment
Surgery is the only treatment that cures medullary thyroid cancer, and getting it right the first time matters more than in most thyroid disease.
- Total thyroidectomy is standard, because C cells are distributed through both lobes
- Removal of the lymph nodes in the central neck compartment is recommended by most guidelines, with the extent of any further node surgery guided by preoperative calcitonin and imaging
- Thyroid hormone replacement is needed afterwards for life, at ordinary replacement doses rather than the suppressive doses used in differentiated cancer
- Radioactive iodine has no role, because these cells do not take up iodine
- For disease that cannot be removed or has spread, treatment is systemic: selective RET inhibitors where a RET change is present, and multi-kinase inhibitors otherwise
- External radiotherapy is used selectively, mainly for local control
Selpercatinib, an oral tyrosine kinase inhibitor approved in 2020, is the best known of the selective RET inhibitors, and its arrival is the main reason the outlook in advanced disease has changed over the past five years.
Survival
Outcomes depend heavily on whether the disease was confined at the time of surgery. Reported five-year survival is around 93 per cent for stages 1 to 3 and about 28 per cent for stage 4. Those figures should be held loosely: because this cancer is rare, survival estimates rest on small numbers, and they describe people treated before selective RET inhibitors were widely available. An individual outlook depends on stage, on how completely the tumour and nodes were removed, on the calcitonin and CEA trend afterwards, and on age and general health.
GLP-1 medications and medullary thyroid cancer
This question now brings many people to the subject, so it deserves a direct answer. GLP-1 receptor agonists used for type 2 diabetes and weight loss carry a boxed warning relating to medullary thyroid cancer, based on C-cell tumours seen in rodents. That warning translates into a firm contraindication: these medicines are not used in anyone with a personal or family history of medullary thyroid cancer or of multiple endocrine neoplasia type 2.
Whether they raise risk in people without that history is a separate question, and the evidence does not support that conclusion. A 2024 review in the journal Thyroid assessed the full body of evidence and found that randomised trials show thyroid cancer occurring rarely and without a consistent increase, that observational studies at higher risk of bias give inconsistent results, and that reporting-based safety signals cannot establish causation. The authors also noted that excessive concern carries its own harm, in the form of unnecessary screening and overdiagnosis. Routine calcitonin testing before starting these medicines is not recommended. What matters is disclosing a personal or family history to the prescriber.
Latest scientific advances
Research over the past three years has concentrated almost entirely on the laboratory side of this disease, which is unusual and useful. The findings below come from peer-reviewed literature and are simplified for general readers; none of them changes what an individual should do without a clinician’s input.
An umbrella review published in 2023, pooling 23 systematic reviews, set out the diagnostic hierarchy plainly. Calcitonin is the most reliable marker for identifying the disease, and the review found no evidence that stimulating it improves on the basal measurement. Carcinoembryonic antigen doubling time was more reliable than calcitonin for identifying people with a poorer prognosis. Ultrasound performed less well than many expect, with only just over half of medullary cancers classified as high risk on standard imaging scoring systems, and cytology alone correctly identified only just over half of cases, which is why measuring calcitonin in needle washout fluid is now considered necessary rather than optional.
A 2026 meta-analysis quantified that last point precisely. Across 13 studies covering 937 patients and 444 medullary lesions, standard needle cytology had a sensitivity of 56 per cent with a specificity of 98 per cent, giving an area under the curve of 0.65. Measuring calcitonin in the needle washout achieved a sensitivity of 98 per cent and a specificity of 97 per cent, with an area under the curve of 1.00. In plain terms, cytology alone rules the disease in but cannot rule it out, whilst the washout test does both. Publication bias was possible for both methods, so the figures are best read as a strong direction rather than exact values.
Work also continues on markers that could complement calcitonin where its measurement is difficult. A 2025 meta-analysis of eight studies covering 4,080 people assessed pro-gastrin-releasing peptide, finding a pooled sensitivity of 74 per cent and specificity of 95 per cent, against 94 per cent and 91 per cent for calcitonin. The conclusion was that it is a useful complementary marker in inconclusive cases, not a replacement, and that assay harmonisation is still needed.
On the question of stimulation testing, a 2025 individual patient data meta-analysis of five studies and 243 patients reached a more nuanced position than the earlier umbrella review. It found the calcium stimulation test performed better in men than in women, proposing thresholds of about 562 picograms per millilitre in men, where sensitivity was 79 per cent and specificity 89 per cent, and about 162 in women, where specificity fell to 66 per cent. The authors positioned it as a tool for highly selected cases with indeterminate basal calcitonin values, with a sex-specific approach, rather than a routine step.
Two further findings bear on surgery. A 2023 meta-analysis of 28 studies confirmed that preoperative calcitonin and CEA levels are among the factors predicting spread to the lateral neck nodes, alongside tumour size, multifocality, capsular invasion, and extension beyond the thyroid, which is why those blood values influence how extensive an operation is planned. Separately, a 2024 systematic review comparing seven sets of surgical guidelines found they vary significantly, that most recommend removing the central neck nodes in all patients, and that these recommendations rest largely on older, low-quality evidence. The authors argued that partial thyroidectomy may eventually become a reasonable option for small, limited tumours, and called for prospective studies.
For advanced disease, a 2025 French consensus on refractory medullary thyroid cancer summarised the molecular picture: a germline RET change in 20 to 25 per cent of cases and an acquired RET change in 70 to 80 per cent of metastatic sporadic cases, which is what makes selective RET inhibition so broadly applicable here. A search of ClinicalTrials.gov in September 2026 returns 12 recruiting interventional studies, including radioligand and immune-based approaches aimed at tumours that no longer respond to existing drugs.
Glossary
| Term | Meaning |
|---|---|
| C cells | Parafollicular thyroid cells that make calcitonin, the origin of this cancer. |
| Calcitonin | The hormone used as the main blood marker for this disease. |
| CEA | Carcinoembryonic antigen, the second marker followed over time. |
| Doubling time | How long a marker takes to double, used to judge disease behaviour. |
| RET | The gene whose alteration drives most medullary thyroid cancers. |
| Germline change | An inherited gene change present in every cell and passed to children. |
| Somatic change | A gene change acquired in the tumour only, not inherited. |
| MEN2 | Multiple endocrine neoplasia type 2, the inherited syndrome involving RET. |
| FNA washout | Measuring calcitonin in fluid rinsed from the biopsy needle. |
Frequently asked questions
What is the tumour marker for medullary thyroid cancer?
Calcitonin is the primary marker, and carcinoembryonic antigen is measured alongside it. Calcitonin is unusual among tumour markers in that it contributes to making the diagnosis rather than only to follow-up. After treatment, both are tracked over time, and how quickly either rises is used to judge how the disease is behaving.
Does a high calcitonin mean I have medullary thyroid cancer?
Not on its own. Kidney disease, proton pump inhibitors, smoking, pregnancy, and several other conditions raise calcitonin, and assay differences also matter. A single raised value is a reason to repeat the test and interpret it with the clinical picture, not a diagnosis. Very high values in someone with a thyroid nodule are a different matter and prompt rapid assessment.
Is medullary thyroid cancer hereditary?
About a quarter of cases are. These are caused by an inherited change in the RET gene, usually as part of multiple endocrine neoplasia type 2. Genetic testing is generally offered to everyone diagnosed, because a positive result has implications for relatives and prompts screening for associated adrenal and parathyroid conditions.
How does it differ from papillary thyroid cancer?
They begin in different cells. Papillary cancer arises from follicular cells, absorbs iodine, is followed with thyroglobulin, and has an excellent outlook. Medullary cancer arises from C cells, does not absorb iodine so radioactive iodine treatment is useless, is followed with calcitonin and CEA, is inherited in up to a quarter of cases, and requires more extensive initial surgery.
Can medullary thyroid cancer be cured?
Yes, when it is confined to the thyroid and neck and is completely removed at the first operation. Reported five-year survival is around 93 per cent for stages 1 to 3. Cure becomes unlikely once the disease has spread to distant sites, where treatment aims to control it, though selective RET inhibitors have changed what control can look like.
Do I need a calcitonin test before starting a GLP-1 medication?
Routine calcitonin testing before starting these medicines is not recommended. What matters is telling your prescriber about any personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2, which is a reason not to use this class of drug at all.
What follow-up is needed after surgery?
Calcitonin and CEA are measured at intervals, with neck ultrasound, and further imaging added if the markers rise. Thyroid hormone replacement is monitored with blood tests. Where an inherited form is confirmed, screening for adrenal and parathyroid involvement continues alongside, and relatives are offered testing.
Sources
- Medullary Thyroid Cancer: What It Is, Symptoms and Treatment — Cleveland Clinic
- Thyroid Cancer Treatment (PDQ) Patient Version — National Cancer Institute, National Institutes of Health
- Multiple endocrine neoplasia — MedlinePlus Genetics, National Library of Medicine
- Cancer Stat Facts: Thyroid Cancer — SEER Programme, National Cancer Institute
- Trimboli P. et al. Diagnostic tests for medullary thyroid carcinoma: an umbrella review — Endocrine, 2023 (indexed in PubMed)
- Zhang J. et al. Fine-needle aspiration cytology and fine-needle aspirate calcitonin measurement for diagnosing medullary thyroid carcinoma: a meta-analysis — Journal of Zhejiang University Medical Sciences, 2026 (indexed in PubMed)
- Ovčariček P.P. et al. Pro-gastrin releasing peptide as a tumour marker of medullary thyroid carcinoma: a comparative bivariate meta-analysis — Clinical Chemistry and Laboratory Medicine, 2025 (indexed in PubMed)
- Sesti F. et al. Role of the calcium stimulation test in diagnosing medullary thyroid cancer: an individual patient data meta-analysis — European Thyroid Journal, 2025 (indexed in PubMed)
- Lin X. et al. Risk factors for cervical lymph node metastasis in medullary thyroid carcinoma: a systematic review and meta-analysis — European Archives of Oto-Rhino-Laryngology, 2023 (indexed in PubMed)
- Cohen O. et al. Initial surgical management of sporadic medullary thyroid cancer: Guidelines based optimal care, a systematic review — Clinical Endocrinology, 2024 (indexed in PubMed)
- Lasolle H. et al. ENDOCAN-TUTHYREF network consensus recommendations: refractory medullary thyroid cancer — Annales d’Endocrinologie, 2025 (indexed in PubMed)
- Espinosa De Ycaza A.E. et al. Glucagon-Like Peptide-1 Receptor Agonists and Thyroid Cancer: A Narrative Review — Thyroid, 2024 (indexed in PubMed)
- Selpercatinib compound record (CHEMBL4559134) — ChEMBL, EMBL-EBI
Other articles
- Calcitonin Blood Test: Levels and What They Mean
- CEA Blood Test: How to Read Your Results
- Thyroid Cancer: Symptoms, Types, Tests, and Survival
- Thyroid Nodule Blood Test: What TSH Really Decides
- TSH Blood Test: How to Read Your Thyroid Results
- Normal Thyroid Levels: How to Read Your Results
- Calcium Blood Test: What Your Levels Mean
- PTH Blood Test: Reading Your Results With Calcium
Calcitonin and CEA are among the lab values where a single number tells you very little and the trend tells you almost everything. Understand your lab results with AI DiagMe, which reads your report line by line and explains each value in plain language, with interpretation reviewed by a committee of physicians.
