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What is medullary thyroid cancer?
Medullary thyroid cancer is an uncommon type of thyroid cancer that is quite different from the more familiar papillary and follicular thyroid cancers. It begins not in the thyroid cells that make thyroid hormone, but in special cells called C cells (or parafollicular cells) that make a hormone called calcitonin. Because of this, medullary thyroid cancer behaves differently and is managed differently. About one in four cases is hereditary, caused by an inherited change in a gene called RET, and can run in families as part of syndromes known as multiple endocrine neoplasia type 2 (MEN2). The rest occur sporadically, with no family history, though many of these tumors still carry a RET change within the tumor itself. A key feature of this cancer is that the C cells release calcitonin and another marker called CEA into the blood, so doctors can measure these in a simple blood test to detect the cancer, judge how much is present, and follow it over time. Medullary thyroid cancer is important to identify correctly because, unlike most thyroid cancers, it does not respond to radioactive iodine. The cornerstone of treatment is surgery to remove the thyroid and nearby lymph nodes, and modern targeted medicines — especially drugs aimed at the RET gene — have transformed the outlook for advanced disease. Care is coordinated by a team that may include endocrinologists, surgeons, medical oncologists, and radiation oncologists.
The main types
Doctors group medullary thyroid cancer by where it starts and how it behaves:
| Type | What it means, simply |
|---|---|
| Sporadic medullary thyroid cancer | Occurs by chance with no family history, accounting for roughly three out of four cases; usually appears as a single tumor in one part of the thyroid, often in adults. |
| Hereditary medullary thyroid cancer (MEN2) | Caused by an inherited RET gene change passed through families; tends to appear younger and in both lobes, and may come with other endocrine tumors, so relatives are offered genetic testing. |
Staging, in plain terms
Medullary thyroid cancer is staged with the TNM system, which describes the size of the tumor (T), whether it has spread to nearby lymph nodes in the neck (N), and whether it has spread to distant parts of the body such as the liver, lungs, or bones (M). These combine into stages I through IV, where lower numbers mean the cancer is smaller and confined and higher numbers mean wider spread. What makes this cancer distinctive is that doctors also rely heavily on two blood markers — calcitonin and CEA — which the tumor releases. Their levels before surgery reflect how much cancer is present, and how quickly they fall after surgery, or how fast they rise over time (the "doubling time"), gives valuable information about how active the cancer is and the outlook. Doctors also test for RET gene changes: an inherited RET change means family members should be offered testing, and the specific RET change within a tumor can guide which targeted medicine is most likely to work. Together, the stage, the blood markers, and the gene findings shape both the treatment plan and the follow-up.
| TNM (AJCC) plus calcitonin/CEA blood markers and RET gene status | What it generally means |
|---|---|
| Stage I | A small tumor (about 2 cm or less) confined to the thyroid, with no spread to lymph nodes or distant sites — often curable with surgery alone. |
| Stage II | A larger tumor still within the thyroid, or one beginning to grow toward nearby tissue, but without lymph-node or distant spread. |
| Stage III | The cancer has spread to lymph nodes in the central part of the neck near the thyroid, but not to distant parts of the body. |
| Stage IV | The cancer has grown into nearby structures, spread to lymph nodes farther out in the neck, or spread to distant organs such as the liver, lungs, or bones; treatment combines surgery, radiation, and targeted medicines. |
The standard of care
Medullary Thyroid Cancer is almost always treated by a team that may include a surgeon, a medical oncologist, and a radiation oncologist, combining therapies for the best result. The usual building blocks are:
Surgery
Removing the entire thyroid (total thyroidectomy) along with nearby lymph nodes is the main treatment and offers the best chance of cure, especially when the cancer is caught early and confined to the neck.
RET-targeted therapy
For advanced or spreading cancer driven by a RET gene change, modern pills that block RET (selective RET inhibitors) can shrink tumors and control the disease, often with fewer side effects than older drugs.
Radiation therapy
Focused external-beam radiation helps control cancer that cannot be fully removed by surgery, treats areas at high risk of return in the neck, and relieves symptoms from tumors that have spread to bone or other sites.
Thyroid hormone replacement
After the thyroid is removed, a daily thyroid hormone pill replaces what the body needs; unlike other thyroid cancers, the dose simply keeps levels normal rather than being pushed to suppress the cancer.
Marker monitoring and genetic counseling
Regular calcitonin and CEA blood tests track the cancer over time, and genetic counseling with RET testing identifies hereditary cases so at-risk relatives can be screened and protected early.
How radiation treatment works
Radiation therapy uses focused high-energy beams to damage the DNA inside cancer cells so they can no longer grow and divide. Medullary thyroid cancer has an important difference from most thyroid cancers: it does not absorb radioactive iodine, the internal radiation used so effectively for papillary and follicular thyroid cancer. That is because the cancer arises from C cells, which do not take up iodine the way ordinary thyroid cells do. As a result, the radiation used for medullary thyroid cancer is external-beam radiation — precise beams aimed from outside the body. Surgery remains the main treatment, but external-beam radiation has a valuable role. When a tumor cannot be completely removed, or when there is a high risk that it will return in the neck after surgery, radiation to the neck and surrounding lymph-node areas can improve local control. Modern techniques such as intensity-modulated radiation therapy (IMRT) shape the dose carefully around the tumor while protecting the windpipe, the swallowing structures, and the spinal cord. When the cancer has spread to distant sites such as bone, focused stereotactic radiation or short palliative courses can control those spots and relieve pain. Because medullary thyroid cancer is often driven by the RET gene, radiation is increasingly used alongside RET-targeted medicines that control disease throughout the body, while radiation handles specific trouble spots. Your radiation oncologist tailors the dose and technique to the location of the cancer and your overall plan.
The main ways radiation is delivered for medullary thyroid cancer:
Intensity-modulated radiation therapy (IMRT)
Shapes radiation beams precisely around the neck to treat areas at risk while sparing the windpipe, swallowing structures, and spinal cord, used when cancer cannot be fully removed or has a high chance of returning.
Stereotactic body radiation therapy (SBRT)
Delivers a high, sharply focused dose in one to a few sessions to small areas of spread, such as a tumor in the bone, lung, or liver, controlling it durably while sparing nearby tissue.
Palliative radiation
Short courses of radiation relieve pain or pressure from tumors that have spread, such as to the bones, improving comfort and function.
Targeted radiopharmaceuticals (selected cases)
In specialized centers, radioactive treatments that home to medullary thyroid cancer cells are being studied to deliver radiation from within the body to sites of spread.
Latest studies shaping care
Care keeps improving — often toward getting the same excellent results with less burden on patients. A few developments:
Selective RET inhibitors transform advanced disease: Newer pills designed to block the RET gene have shown strong, lasting tumor shrinkage in advanced medullary thyroid cancer with fewer side effects than older multi-target drugs, becoming a standard option for RET-driven disease.[1]
Selective RET inhibitor clinical trials
Calcitonin and CEA doubling time predicts outlook: Research confirmed that how quickly the blood markers calcitonin and CEA rise after treatment is a powerful guide to how active the cancer is and helps doctors decide when to intensify monitoring or treatment.[2]
Medullary thyroid cancer biomarker studies
Radiation for neck control after surgery: Studies support external-beam radiation to the neck for selected patients at high risk of the cancer returning locally, improving control in the neck when surgery alone may not be enough.[3]
Postoperative neck radiation series
Common questions
Why won't radioactive iodine work for medullary thyroid cancer? Radioactive iodine works only on cells that absorb iodine, like the ordinary thyroid cells that cause papillary and follicular cancers. Medullary thyroid cancer starts in C cells, which do not take up iodine, so radioactive iodine is not effective. When radiation is needed, doctors use precise external-beam radiation instead.
Should my family be tested if I have medullary thyroid cancer? Often, yes. About a quarter of cases are hereditary and caused by an inherited RET gene change. Genetic counseling and a RET test can tell whether your cancer is hereditary; if it is, close relatives can be tested and, if they carry the change, screened and protected early — sometimes even before cancer develops.
What do the calcitonin and CEA blood tests tell us? These are markers the cancer releases into the blood. Their levels reflect how much cancer is present, and tracking them over time — especially how fast they rise — helps doctors judge how active the cancer is, whether treatment is working, and when more treatment may be needed.
References
Numbered sources for the studies cited above. Links open the primary publication on PubMed or the publisher’s site.