Metastatic Thyroid Cancer: What to Ask

"Thyroid cancer" covers several diseases that behave nothing alike. The first question is which one.

NCI's summary works through them separately. Papillary, follicular, Hurthle cell and poorly differentiated cancers are grouped as differentiated disease. Medullary thyroid cancer is different in origin and is followed with different blood tests. Anaplastic thyroid cancer is different again, and it moves fast.

A person with metastatic papillary cancer and a person with metastatic anaplastic cancer are having two unrelated conversations. Getting the exact wording from the pathology report is the starting point.

Differentiated thyroid cancers often keep the ability to soak up iodine. That is what makes radioactive iodine work at all.

When that stops, the cancer is called radioiodine-refractory, or RAI-refractory. NCI uses that status as the gateway to systemic drugs.

Look at how the trials defined who could enter. SELECT enrolled people with differentiated thyroid cancer. They had to be RAI-refractory. And their scans had to show growth in the previous 13 months. DECISION used a similar rule, with growth within the past 14 months.

That second criterion matters. Both trials required the cancer to be growing, not merely present. Some metastatic differentiated thyroid cancer sits still for a long time.

SELECT randomized 261 people to lenvatinib at 24 mg daily and 131 to placebo. That is the trial's full starting amount; in practice many people are started lower or cut back, and your endocrinologist or oncologist decides what you take.

Median progression-free survival was 18.3 months on lenvatinib. On placebo it was 3.6 months. The hazard ratio was 0.21. The response rate was 64.8% against 1.5%. Overall survival was not significantly different, at a hazard ratio of 0.73. The trial let placebo patients cross over, which blurs that figure.

The toxicity number deserves equal billing. Treatment-related adverse events of any grade occurred in 97.3% of the lenvatinib group.

DECISION randomized 417 people. They received sorafenib twice daily at its standard trial amount, or placebo. Median progression-free survival was 10.8 months against 5.8 months. The hazard ratio was 0.59. Again, overall survival was not significantly improved.

Neither drug cures. Both delay progression, and both cost something in side effects. That trade is the actual decision.

Before settling on a multikinase inhibitor, it is worth knowing whether a targeted option applies.

For RET fusion-positive thyroid cancer, NCI describes LIBRETTO-001. Nineteen such patients were enrolled. Most took the phase II amount of selpercatinib, twice daily. The objective response rate was 79%. At one year, 71% of responses were still going.

Pralsetinib is discussed for RET as well. NTRK fusions bring larotrectinib and entrectinib into range. These are rare findings, but they are worth ruling in or out before a broader drug is chosen.

The practical question is whether the testing is finished, and whether anything is still pending.

Medullary thyroid cancer arises from the calcitonin-producing cells. That gives it a marker no other thyroid cancer has.

NCI notes that calcitonin can be detectable in blood even when the tumor is clinically hidden. It also gives a caution: a modest calcitonin rise can produce a false-positive diagnosis, so RET genetic testing is used to sort it out. Family members may be screened for calcitonin elevation and for the RET variant.

Treatment evidence here is separate too. The EXAM trial randomized 330 people with metastatic medullary thyroid cancer. All had growth on imaging. They were assigned 2 to 1 to cabozantinib daily, at the trial's amount, or placebo. Crossover was not allowed.

Median progression-free survival was 11.2 months against 4.0 months, with a hazard ratio of 0.28. The response rate was 28%, all partial. Overall survival showed no significant difference at interim analysis. Grade 3 or 4 adverse events hit 69% of the cabozantinib group and 33% of the placebo group. Sixteen percent stopped the drug because of side effects.

For RET-altered medullary cancer already treated with vandetanib or cabozantinib, LIBRETTO-001 reported a 69% response rate on selpercatinib, with 9% complete responses. At one year, 86% of responses were ongoing.

Inherited RET variants cause MEN2, and NCI's summary raises pheochromocytoma in that context. That is a reason germline testing is not a footnote.

This subtype is measured in weeks rather than months, and the testing has to keep up.

NCI states that molecular testing for the BRAF V600E variant is advised in anaplastic thyroid cancer. The reason is a specific approval.

A phase II trial included 16 patients with anaplastic thyroid cancer and a BRAF V600E variant. They received dabrafenib plus trametinib. The confirmed response rate was 69%. Median duration of response was not reached, nor was median survival. Twelve-month estimates were 90% for duration of response, 79% for progression-free survival and 80% for overall survival.

FDA approved the combination on that basis, for unresectable or metastatic anaplastic thyroid cancer with the BRAF V600E variant.

Sixteen patients is a small number. It is still the difference between a targeted option and none, which is why the speed of the test matters.

Radioactive iodine is not unlimited, and the total received matters.

NCI notes two ways to raise TSH before a dose is given: withdrawing thyroid hormone, or giving recombinant human thyrotropin. It records that recombinant thyrotropin preserves quality of life and lowers the radiation dose to the rest of the body, compared with hormone withdrawal.

It is also candid about limits. In low-risk disease, the role of radioiodine is unclear, because no disease-free or 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, over 10.3 years of follow-up.

None of that changes metastatic care directly. It does explain why a team may weigh a further dose carefully rather than repeating it by default.

For the disease overall, see thyroid cancer. For what molecular testing involves, see biomarker testing and precision medicine. For symptom-directed support alongside treatment, see palliative care.

Two things drive urgency here: a neck mass that can press on the airway, and the side effects of the kinase inhibitors used in this setting.

• Call 911 or go to an emergency department if you cannot breathe properly, are making a noisy or high-pitched sound when you breathe in, or are choking. A thyroid cancer growing in the neck can narrow the windpipe, and anaplastic disease can do this over days.
• Call 911 or go to an emergency department if you are on lenvatinib and have chest pain, weakness or numbness on one side of the face or body, sudden severe headache, slurred speech, sudden vision change, or a seizure. The drug label lists these as emergencies.
• Call 911 or go to an emergency department if you are coughing up blood or blood clots, vomiting blood, or passing black tarry stools. Bleeding is a known lenvatinib risk.
• Call your care team the same day if a neck lump is clearly growing, or you have new hoarseness, pain on swallowing, or food sticking. These are the thyroid cancer symptoms NCI lists, and in metastatic disease they can mean local pressure.
• Call your care team the same day if you have severe stomach pain on a kinase inhibitor, or a surgical or radiation wound that opens or will not heal.
• Call your care team within a day or two if you have diarrhea or vomiting you cannot keep on top of, or you feel weak, confused, or dehydrated. The lenvatinib label names dehydration as a reason to make contact.

• NCI PDQ — Thyroid Cancer Treatment (Health Professional Version)
• NCI PDQ — Thyroid Cancer Treatment (Patient Version), accessed August 11, 2026
• MedlinePlus, Lenvatinib, accessed August 11, 2026