Medullary thyroid cancer starts in the cells that produce calcitonin

Medullary thyroid cancer (MTC) is a rare form of thyroid cancer that begins in the C cells of the thyroid gland. These cells produce a hormone called calcitonin, which helps regulate calcium levels in your blood. When C cells become cancerous, they grow abnormally and can spread to lymph nodes and other parts of the body.

MTC accounts for about 3 to 5 percent of all thyroid cancers. Unlike the more common papillary or follicular thyroid cancers, medullary cancer behaves differently and requires different treatment. It is more likely to spread early and can be harder to detect in its early stages because calcitonin levels may rise before a lump appears in the thyroid.

About 25 percent of medullary thyroid cancers are hereditary, meaning they run in families. The other 75 percent occur randomly in people with no family history. Knowing whether your cancer is hereditary matters because it changes what screening your relatives may need and what treatment options your doctor will consider.

Key Takeaways

  • Medullary thyroid cancer grows from C cells in the thyroid and produces calcitonin, a hormone doctors can measure in your blood to track the disease.
  • About one in four cases is hereditary and linked to a gene mutation called RET; the other three in four occur without a family pattern.
  • Symptoms often appear late, so the cancer may have spread before you notice a lump or feel pain in your neck.
  • Calcitonin and CEA (carcinoembryonic antigen) blood tests are the main tools doctors use to detect MTC and monitor whether treatment is working.
  • Surgery to remove the thyroid is the primary treatment, and whether lymph nodes are removed depends on how far the cancer has spread.

How medullary thyroid cancer differs from other thyroid cancers

The thyroid has several types of cells, and each type can become cancerous in a different way. Papillary thyroid cancer, the most common form, grows slowly and usually stays in the thyroid or nearby lymph nodes. Follicular thyroid cancer also tends to grow slowly. Medullary cancer behaves more aggressively—it spreads to lymph nodes earlier and can reach distant organs like the lungs, liver, and bones.

Another key difference is how doctors track the disease. With papillary or follicular cancer, doctors use radioactive iodine scans and thyroid hormone levels to monitor you. With medullary cancer, radioactive iodine does not work because C cells do not absorb iodine the way other thyroid cells do. Instead, doctors measure calcitonin and another marker called CEA (carcinoembryonic antigen) in your blood. Rising levels of these markers signal that cancer is present or returning.

Medullary cancer is also the only thyroid cancer that can be part of a hereditary syndrome. Some people inherit a mutation in the RET gene that makes medullary thyroid cancer almost certain to develop at some point in life. This hereditary form often appears earlier than sporadic MTC and may occur alongside other tumors in the adrenal glands or parathyroid glands.

Hereditary versus sporadic medullary thyroid cancer

If you have medullary thyroid cancer, your doctor will likely recommend genetic testing to see whether you carry a RET gene mutation. This matters because it tells you whether your relatives are at risk. If you have the mutation, your siblings, children, and parents should be tested. If they carry the mutation too, they may need preventive surgery or close monitoring even if they have no symptoms.

Hereditary medullary thyroid cancer is part of a condition called Multiple Endocrine Neoplasia type 2 (MEN2). People with MEN2 can develop medullary thyroid cancer, pheochromocytoma (a tumor in the adrenal gland), and hyperparathyroidism (overactive parathyroid glands). The age at which cancer develops and how aggressive it is depends on which specific RET mutation you have. Some mutations carry higher risk than others, and your doctor can use this information to guide how often you need screening.

Sporadic medullary thyroid cancer—the kind without a family history—occurs when a RET mutation happens randomly in a single cell during your lifetime. It is not inherited, so your children will not automatically be at risk. However, your doctor will still recommend genetic testing to confirm whether your cancer is truly sporadic or whether you carry a mutation that could affect your family.

Symptoms and how medullary thyroid cancer is often found

Many people with early medullary thyroid cancer have no symptoms at all. The cancer may be discovered by chance during imaging for another reason, or it may be found because a routine blood test shows elevated calcitonin. Some people notice a lump in the neck, hoarseness, difficulty swallowing, or neck pain, but these symptoms usually appear only after the cancer has grown or spread.

Because symptoms come late, medullary thyroid cancer is sometimes found at an advanced stage. This is one reason why genetic testing is so important in families with a history of MTC. If you know you carry a RET mutation, your doctor can monitor your calcitonin levels regularly and catch cancer early, before you feel any symptoms. In hereditary cases, preventive thyroid removal is often recommended in childhood or early adulthood, before cancer has a chance to develop.

In sporadic cases, the cancer may be found when you see a doctor for neck symptoms, or it may show up on imaging done for an unrelated reason. Once MTC is suspected, your doctor will order calcitonin and CEA blood tests. If these are elevated, imaging such as ultrasound, CT, or MRI will help determine the size and location of the tumor and whether it has spread to lymph nodes or distant organs.

How doctors stage and assess medullary thyroid cancer

Staging tells you how far the cancer has spread and helps your doctor plan treatment. Medullary thyroid cancer is staged from 1 to 4, with stage 1 being the smallest tumors confined to the thyroid and stage 4 meaning the cancer has spread to distant organs. Your stage depends on the size of the tumor, whether lymph nodes are involved, and whether distant spread has occurred.

Calcitonin level at diagnosis also matters. A very high calcitonin level suggests the cancer may be more advanced or more aggressive, even if imaging does not show obvious spread. Your doctor will use calcitonin and CEA levels as a baseline to compare against future tests. If these markers drop after surgery, it is a good sign. If they stay high or rise over time, it suggests cancer remains or is returning.

Imaging studies help locate the tumor and check for spread. Ultrasound of the thyroid is usually the first step. If cancer is suspected, CT or MRI of the neck and chest may follow. Some patients need additional imaging such as a bone scan or PET scan to look for spread to distant sites. Your doctor may also recommend a test called a calcitonin stimulation test, which involves injecting a substance to see how much calcitonin your C cells release—a way to detect cancer that may not show up on imaging.

Treatment options for medullary thyroid cancer

Surgery is the main treatment for medullary thyroid cancer. Your surgeon will remove the entire thyroid gland, a procedure called a total thyroidectomy. Whether lymph nodes are removed depends on how far the cancer has spread. If calcitonin levels are very high or imaging shows lymph node involvement, your surgeon may remove lymph nodes in the neck and upper chest as well.

After surgery, your doctor will monitor your calcitonin and CEA levels regularly. If these markers fall to undetectable levels, surgery may have removed all the cancer. If they remain elevated or rise over time, it suggests cancer is still present or has spread. In that case, your doctor may recommend additional imaging or other treatments.

For advanced medullary thyroid cancer that has spread or cannot be removed surgically, targeted therapy and immunotherapy are options. Targeted drugs work by blocking specific proteins that help cancer cells grow. These are not chemotherapy and often have different side effects. Your doctor will discuss which treatments make sense based on your specific situation, the stage of your cancer, and your overall health.

Life after medullary thyroid cancer diagnosis

After surgery, you will need lifelong monitoring. Your doctor will check your calcitonin and CEA levels at regular intervals—how often depends on your stage and how well surgery went. If levels are undetectable, you may need testing every few months at first, then less frequently over time. If levels are elevated, you may need more frequent testing and imaging to look for recurrence or spread.

You will also need thyroid hormone replacement therapy after your thyroid is removed. Your doctor will prescribe levothyroxine, a synthetic thyroid hormone, and adjust the dose based on blood tests. Taking this medication correctly is important for your overall health and may also help slow any remaining cancer cells.

If you have hereditary medullary thyroid cancer, your relatives should be informed and offered genetic testing. Your doctor or a genetic counselor can help explain the risks and what screening options are available. Early detection through monitoring or preventive surgery can make a significant difference in outcomes for family members who carry the RET mutation.

Frequently Asked Questions

Can medullary thyroid cancer be cured?

If the cancer is caught early and confined to the thyroid, surgery often removes it completely, and calcitonin levels return to normal. However, if the cancer has spread to lymph nodes or distant organs, cure is less likely, though treatment can slow growth and extend survival. Your doctor will discuss realistic outcomes based on your stage and how the cancer responds to treatment.

What does a high calcitonin level mean?

Calcitonin is produced by C cells, so a high level indicates C cells are present and active. In someone without thyroid disease, this usually means medullary thyroid cancer. After surgery, a calcitonin level that stays high or rises suggests cancer remains or is returning. Your doctor will use calcitonin trends over time to guide decisions about additional treatment or monitoring.

If I have the RET gene mutation, will I definitely get medullary thyroid cancer?

Not everyone with a RET mutation develops cancer, but the risk is very high—often 90 percent or more depending on the specific mutation. This is why preventive thyroid removal is often recommended in childhood or early adulthood for people with hereditary MTC. Your doctor can explain your specific risk based on which RET mutation you carry.

Do I need to tell my family members about my diagnosis?

If you have hereditary medullary thyroid cancer, your relatives are at risk and should know so they can pursue genetic testing and monitoring. A genetic counselor can help you understand what to tell family members and what screening options are available. If your cancer is sporadic, your relatives do not automatically need testing, but your doctor may still recommend it to be certain.

What happens if medullary thyroid cancer comes back after surgery?

Recurrence is detected through rising calcitonin or CEA levels or through imaging that shows new tumors. Treatment options include additional surgery if the cancer is localized, targeted therapy, or immunotherapy for advanced disease. Your doctor will discuss what is realistic based on where the cancer has returned and your overall health.