The short answer
Four different cancers share the name thyroid cancer. Papillary, follicular, medullary and anaplastic behave nothing alike, and each has its own treatment list. For the first two, age 55 is written into the staging system.
The cell type comes before the stage number. Papillary, follicular, medullary and anaplastic are handled separately.
Radioactive iodine only works on differentiated cancers. Medullary and anaplastic thyroid cancer do not take it up.
Age 55 is a formal cut-off in the staging system for differentiated thyroid cancer, and nobody under 55 can be staged above II.
Anaplastic thyroid cancer is always stage IV, and about a quarter of cases carry a BRAF V600E change.
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The full explanation.
Four different cancers share one name
Thyroid cancer is not one disease. NCI's treatment summary is organised by cell type, not by stage, because the types behave nothing alike.
- Papillary and follicular are the differentiated types. They are the common ones, and they are usually curable.
- Medullary thyroid cancer starts in a different cell. NCI calls it a neuroendocrine cancer with an intermediate outlook.
- Anaplastic thyroid cancer is the undifferentiated one. It grows fast, spreads early, and has a poor outlook.
So the first question is not "what stage". It is "what does the pathology say". Almost every later decision follows from that answer.
This page explains what each type usually involves. It is not advice about your own treatment.
Papillary and follicular: surgery comes first
For localised or regional disease, NCI lists surgery, radioactive iodine, thyroid-suppression therapy and external radiation as the options.
The surgical choice is between removing the whole gland and removing one lobe. NCI says survival is similar in early-stage disease, but complication and local recurrence rates differ.
Total thyroidectomy is often chosen. Papillary cancer is frequently present in both lobes, and removing everything makes later monitoring cleaner. In a review of 52,173 people in a national database, tumours under 1 cm did just as well either way. For tumours 1 cm or larger, lobectomy carried a higher risk of recurrence and death.
Lobectomy alone may be enough for a small papillary cancer under 1 cm that is low risk, in one spot, confined to the thyroid, with no involved neck nodes and no past radiation to the head or neck. About 5 to 10 percent of people have a later recurrence in the remaining thyroid.
Involved neck nodes are removed at the same operation. NCI notes this lowers the recurrence rate but has not been shown to improve survival.
The radioactive iodine question
Differentiated thyroid tissue absorbs iodine. That is why iodine I 131 can treat it from the inside. Medullary and anaplastic cancers do not do this, so the treatment is useless for them.
Radioactive iodine has two purposes. It destroys leftover normal thyroid tissue, which makes thyroglobulin blood tests more meaningful. And it treats cancer that has spread.
It is not automatic. NCI says the role in low-risk disease is unclear, because neither disease-free nor overall survival benefit has been shown. One review of 1,298 low-risk patients from the French Thyroid Cancer Registry found no difference in either measure after 10.3 years.
The decision uses tumour size, blood vessel invasion, capsule invasion and how many nodes are involved. Long-term risks include second cancers and damage to the salivary and tear glands.
Nearly everyone who has the whole gland removed then needs thyroid hormone. The dose is often set higher than replacement to push TSH down. NCI notes this seems to improve progression-free survival, but there is no definite proof it improves overall survival. How far to push it depends on recurrence risk and on other health problems.
Why age 55 is written into the stage
Differentiated thyroid cancer has a staging quirk found almost nowhere else. Age is part of the stage.
A study of 1,807 people found distant spread the strongest predictor of survival, followed by age, with 55 the best cut-off. A later study of 9,484 people confirmed it. The AJCC 8th edition moved the line from 45 to 55.
The practical effect is large. Someone under 55 cannot be staged above II, even with cancer in the lungs or bones. Stages III and IV only exist for people 55 and over. So a stage II diagnosis means very different things at 30 and at 70.
When iodine stops working
Some cancers stop taking up iodine. NCI calls this iodine-refractory or iodine-resistant disease, and the options change.
Two drugs have randomised evidence here. Sorafenib is approved for locally recurrent or metastatic differentiated thyroid cancer that is refractory to radioactive iodine. In the DECISION trial, median progression-free survival was 10.8 months against 5.8 months on placebo. Lenvatinib is approved for the same setting, and in the SELECT trial median progression-free survival was 18.3 months against 3.6 months. Both cause frequent side effects. In SELECT, grade 3 or higher events occurred in about 76 percent of people taking lenvatinib.
Cabozantinib is approved for people aged 12 and over whose differentiated thyroid cancer has progressed after earlier VEGFR-targeted treatment.
NCI advises genomic testing for actionable changes such as RET and NTRK fusions in advanced progressive disease. Selpercatinib is approved for advanced thyroid cancer with a RET fusion that is iodine-refractory. Larotrectinib and entrectinib target NTRK fusions across tumour types.
Pralsetinib is also approved for RET fusion-positive iodine-refractory thyroid cancer. Its earlier approval for RET-altered medullary thyroid cancer was withdrawn in 2023, and its current label no longer carries that indication.
Medullary thyroid cancer follows a different track
Medullary thyroid cancer starts in the calcitonin-producing C cells. Calcitonin is used as a blood marker.
For localised disease, NCI lists total thyroidectomy, with external radiation as an option. Radioactive iodine has no role.
For locally advanced or metastatic disease, the options are targeted therapy and palliative chemotherapy. Vandetanib and cabozantinib both have randomised evidence. In one trial of 331 people, median progression-free survival was 30.5 months with vandetanib against 19.3 months with placebo. Selpercatinib is approved for advanced medullary thyroid cancer with a RET mutation, in adults and children aged 2 and over. A trial comparing first-line selpercatinib with cabozantinib or vandetanib reported a 12-month progression-free survival rate of 86.8 percent against 65.7 percent.
NCI adds that some people with distant spread live a long time and can be watched until symptoms appear. No single chemotherapy regimen counts as standard here.
Anaplastic thyroid cancer is always stage IV
Every anaplastic thyroid cancer is classed as stage IV, whatever its size. The subdivisions IVA, IVB and IVC describe how far it has grown, not whether it is advanced.
It must be told apart carefully from lymphoma, which can look similar. Surgery is only possible when the disease is still confined, which is rare, and a tracheostomy is often needed. External radiation is used when surgery is not possible.
About 25 percent of anaplastic thyroid cancers carry a BRAF V600E change, and NCI advises testing for it. In a phase II trial of 16 people with that change, dabrafenib plus trametinib gave a confirmed response rate of 69 percent, and the FDA approved the combination for unresectable or metastatic BRAF V600E anaplastic thyroid cancer.
Numbers to hold loosely
SEER reports five-year relative survival of 98.3 percent for thyroid cancer overall for 2016 through 2022. By stage at diagnosis it is 99.9 percent for localised, 98.1 percent for regional and 48.3 percent for distant disease.
Those figures pool all four cell types, and papillary cancer dominates the count. They tell you little about anaplastic or medullary disease. Ask your team what the figures look like for your type.
When to get help sooner
- Call 911 or go to an emergency department if breathing becomes difficult or noisy, or the airway feels like it is tightening. Anaplastic thyroid cancer can press on the windpipe quickly.
- Call 911 or go to an emergency department if you have a seizure, or muscle spasms that affect your breathing, after thyroid surgery. These can be signs of a very low blood calcium level.
- Call your care team the same day if swallowing is getting harder quickly, a neck lump is growing over days rather than months, or your voice becomes hoarse or suddenly worse.
- Call your care team within a day or two if you get tingling in the lips, fingers or toes, or muscle cramps, after thyroid surgery. Low calcium is common after the gland is removed and is treatable.
Related pages
Thyroid Cancer, Thyroid Cancer Types, Thyroid Cancer Stages, and What Does an NTRK Fusion Mean?.
Sources
- https://www.cancer.gov/types/thyroid/hp/thyroid-treatment-pdq
- https://seer.cancer.gov/statfacts/html/thyro.html
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f4bedd21-efde-44c6-9d9c-b48b78d7ed1e
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7fa848ba-a59c-4144-9f52-64d090f4d828
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=16edd46e-28b8-f06d-e063-6394a90ae31b
- https://www.cancer.gov/types/thyroid/patient/thyroid-treatment-pdq
- https://medlineplus.gov/ency/article/000385.htm
Words to know
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Common questions
Why does my stage depend on my age?
For papillary and follicular thyroid cancer only. An analysis of 9,484 people supported age 55 as the cut-off, and the AJCC 8th edition moved the line from 45 to 55. Below 55 the highest possible stage is II, even with spread to distant sites.
Do I definitely need radioactive iodine after surgery?
Not always. NCI says the role of radioactive iodine in low-risk disease is unclear, because no survival or disease-free survival benefit has been shown. One French registry review of 1,298 low-risk patients found no difference either way.
Why is anaplastic thyroid cancer treated so urgently?
It grows fast and invades nearby structures. NCI notes death is usually from uncontrolled cancer in the neck, often within months. A tracheostomy is frequently needed, and testing for a BRAF V600E change is advised.
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Sources last checked: 2026-08-16 what this meansLast updated: 2026-08-17Next planned review: 2027-01-20
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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