Learning Center: Thyroid Cancer Outcomes, Radioactive Iodine for Intermediate-Risk Cancer
For thyroid cancer that has spread to nearby lymph nodes or grown just outside the thyroid, it is not known for certain whether radioactive iodine after surgery improves survival or lowers recurrence. No randomized trial has reported results for this group. The studies that exist point in different directions, and the reasons are explained here.
Who this page is about
Last reviewed: November 8, 2026
This page covers adults with papillary or follicular thyroid cancer who had a total thyroidectomy and whose cancer was in the "intermediate risk" group of the American Thyroid Association. In plain words, that usually means one or more of:
small amounts of growth into the tissue just outside the thyroid, seen under the microscope
spread to lymph nodes in the neck
a more aggressive microscopic type, or tumor cells invading blood vessels
Low-risk cancer, where two randomized trials exist, is covered on Radioactive Iodine for Low-Risk Cancer. Spread to the lungs, bones or other organs is covered on Thyroid Cancer With Distant Spread. The Radioactive Iodine Ablation page explains the treatment itself.
Why there is no survival curve on this page
The other pages in this series show redrawn survival curves. This one does not, on purpose. The only curves available for this group come from records of past patients, where the people who received radioactive iodine differed from those who did not in ways the records do not capture. Drawing those curves side by side would suggest a fair comparison that the studies cannot provide.
What the studies found
| Study | People | What was measured | Result |
|---|---|---|---|
| National Cancer Database, USA (1998-2006)[1] | 21,870 with intermediate-risk papillary cancer; 70.5% received radioactive iodine | Deaths from any cause | 29% lower risk of death with radioactive iodine after adjustment (hazard ratio 0.71) |
| National cancer registry (SEER), USA (2010-2015)[2] | 4,275 with papillary cancer spread to lymph nodes in the side of the neck | Deaths from any cause, and deaths from causes other than thyroid cancer | Radioactive iodine appeared to lower deaths from causes it cannot affect (hazard ratio 0.71), a sign that the apparent benefit reflects who received it |
| Samsung Medical Center, Korea (1997-2015)[3] | 8,297 with intermediate-risk papillary cancer; 90.2% received radioactive iodine | Recurrence in the neck | No significant difference after adjustment (hazard ratio 0.85), including in people with lymph node spread or growth outside the thyroid |
| IoN randomized trial, UK, subgroups[4] | People in the trial with slightly larger tumors growing just outside the thyroid, or with small central lymph node spread | Recurrence | Recurrence was higher in these subgroups (9% and 13%) than in others, but similar with or without radioactive iodine; the authors drew no conclusion from these small groups |
Why the registry results may be misleading
The large national study found that people who received radioactive iodine lived longer.[1] But it measured deaths from any cause, and very few people with this kind of thyroid cancer die of it. Most deaths were from heart disease, other cancers and old age.
A 2026 study tested this directly. It looked at deaths from causes other than thyroid cancer, such as heart disease, which radioactive iodine cannot prevent. People who received radioactive iodine still appeared to be protected from those deaths, by almost exactly the same amount (hazard ratio 0.71).[2] This suggests that people who received radioactive iodine were healthier, younger, or had better access to care to begin with. The authors concluded that registry data can neither confirm nor rule out a benefit.
What the hospital study found about recurrence
The Korean study looked at the cancer coming back in the neck, which is the outcome most likely to show a difference. After accounting for tumor features, radioactive iodine was not linked to fewer recurrences, including in people with BRAF-positive tumors, tumors over 1 cm, lymph node spread, or growth outside the thyroid. Higher doses did not lower recurrence either.[3] Because nine in ten people in that study received radioactive iodine, the group without it was fairly small.
Other outcomes
Side effects, quality of life and the days of limited close contact after treatment are described on Radioactive Iodine for Low-Risk Cancer, using results from the IoN trial. The doses used for intermediate-risk cancer are sometimes higher, so side effects such as dry mouth and changes in taste may be more common than in that trial.
Key points
No randomized trial has yet reported whether radioactive iodine helps intermediate-risk thyroid cancer.
A large registry study linked radioactive iodine to longer life, but a later study showed the same apparent "benefit" for deaths radioactive iodine cannot affect, which points to differences between the groups.
A large hospital study and the IoN trial subgroups found similar recurrence with or without radioactive iodine.
Decisions in this group are made person by person, weighing tumor features, blood tests and scans after surgery, and the person's own preferences.
References
Ruel E, Thomas S, Dinan M, et al. Adjuvant radioactive iodine therapy is associated with improved survival for patients with intermediate-risk papillary thyroid cancer. J Clin Endocrinol Metab. 2015;100(4):1529-1536. doi:10.1210/jc.2014-4332 PubMed 25642591
Liu T, Qiao J, Mao M, et al. Apparent survival benefit of postoperative radioactive iodine in lymph node-positive papillary thyroid carcinoma: a negative-control analysis for unmeasured confounding. Cancer Med. 2026;15(10). doi:10.1002/cam4.72320 PubMed 42910564
Kim SK, Woo JW, Lee JH, et al. Radioactive iodine ablation may not decrease the risk of recurrence in intermediate-risk papillary thyroid carcinoma. Endocr Relat Cancer. 2016;23(5):367-376. doi:10.1530/ERC-15-0572 PubMed 26917553
Mallick U, Newbold K, Beasley M, et al. Thyroidectomy with or without postoperative radioiodine for patients with low-risk differentiated thyroid cancer in the UK (IoN): a randomised, multicentre, non-inferiority trial. Lancet. 2025;406(10498):52-62. doi:10.1016/S0140-6736(25)00629-4 PubMed 40543520
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