OnCo
trialsTrialPositive

IoN

The UK trial confirming that low-risk thyroid cancer patients can safely avoid radioactive iodine, published in 2025.

Lancet 2025: recurrence-free rates 98% without and 96% with radioiodine at 5 years; non-inferiority met, extending the ESTIMABL2 finding to pT2 tumours. Guideline bodies now recommend against routine ablation in this group.

Setting
Low-risk differentiated thyroid cancer (pT1-T2, N0/Nx, no adverse features) after thyroidectomy: no radioiodine vs radioiodine ablation
Phase
Phase 3
Sponsor
Cancer Research UK / UCL
Registry
NCT01398085
Headline result
5-year recurrence-free ~98% (no RAI) vs ~96% (RAI).
Reported
2025
Enrolled
504
Replication
Replicates ESTIMABL2.

Outcomes

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In plain words
What these results mean for people, not percentages
504 people took part
Recurrence-free at 5 yearsprimarysurrogate endpoint
  • 98 vs 96 out of 100 alive without the cancer coming back at 5 years with No radioiodine compared with Radioiodine; 2 more per 100.
  • Roughly one extra person helped for every 50 treated. That is a rough figure taken from the two percentages, not a guarantee for any one person.
  • This is a surrogate endpoint: it measures the cancer being controlled or absent on scans and tests, which often, but not always, translates into living longer.
  • These results apply to the people the trial enrolled: Low-risk differentiated thyroid cancer (pT1-T2, N0/Nx, no adverse features) after thyroidectomy: no radioiodine vs radioiodine ablation. People in a different situation may not see the same effect.

Numbers are from the trial as recorded here; see the source links in the table below. This is orientation, not medical advice: ask your team how closely the trial population matches you.

504 participants enrolled.

Recurrence-free at 5 yearsprimary
No radioiodine98 of 100
Radioiodine96 of 100
Source
EndpointArmnValueHR (95% CI)pSource
Recurrence-free at 5 yearsprimaryNo radioiodine—98%——link
Radioiodine—96%
Replication
Replicates ESTIMABL2.

Connected

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Pages like this

not linked directly; found by shared links

cancers

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Thyroid cancer

technologies

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Radioiodine therapy and whole-body iodine scanning

drugs

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ApprovedRadiopharmaceutical (beta/gamma emitter, natural uptake)
Radioactive iodine (I-131) · Sodium iodide I-131

institutions

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Cancer Research UK

terms

1
Low-risk differentiated thyroid cancer (ATA risk)