Medullary Thyroid Cancer, from the CureRays guide library.

Medullary thyroid cancer starts in the thyroid's hormone-making C cells, is tracked with the blood markers calcitonin and CEA, is often linked to the RET gene, and is treated mainly with surgery — with radiation and targeted pills for harder-to-control disease.

What it is.

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.

How radiation treats it.

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 ways we can treat it.

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.

Questions we hear often.

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.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.