Thyroidectomy with or without postoperative radioiodine for patients with low-risk differentiated thyroid cancer in the UK (IoN): a randomised, multicentre, non-inferiority trial
Authors' conclusion
The IoN trial shows that ablation (or postoperative radioiodine) can be avoided for patients with pT1, pT2, and N0 or Nx tumours with no adverse features. Many patients with low-risk differentiated thyroid cancer worldwide can safely avoid postoperative radioiodine and its related hospitalisation and side-effects, which in turn results in lower health-care costs.
Study context
- Population
- Low-risk DTC with R0 resection after total thyroidectomy; pT1, pT2, pT3 (TNM7) or pT3a (TNM8); N0, Nx or N1a; 33 UK cancer centresITT population
- Participants
- 504 participants
- Comparison
- No ablation vs 1.1 GBq radioiodine ablation after total thyroidectomy
- No ablationn = 251
- Ablationn = 253reference
- Primary endpoint
- Recurrence-free survival (no locoregional recurrent or persistent structural disease, distant metastases or death from thyroid cancer)
- Follow-up
- 5 years
Methodological detailsmulticentre, non-inferiority, phase 3, minimisation (1:1), Stratified by centre, age, T stage and nodal status, Annual neck US and 6-monthly serum Tg
- Multicentre
- Non-inferiority
- Phase 3
- Minimisation (1:1)
- Stratified by centre, age, T stage and nodal status
- Annual neck US and 6-monthly serum Tg
Primary result
5-year recurrence-free rate
Absolute risk difference
0.5 percentage points
95% CI −2.2 to 3.2
P = 0.033 for non-inferiority
By group
Between No ablation and Ablation
absolute risk difference 0.5 percentage points (95% CI −2.2 to 3.2); P for non-inferiority = 0.033
As reported in the abstract
Further findings
| Outcome | No ablation | Ablation |
|---|---|---|
| 5-year recurrence-free rate, per-protocol analysis · per-protocol analysis | 97.9% (CI 96.1–99.7) | 96.9% (CI 94.7–99.1) |
| Recurrences during follow-up (ITT) · median follow-up 6.8 years (IQR 5.6-8.6) no ablation; 6.6 years (4.8-8.5) ablation | 8 events | 9 events |
- Recurrences during follow-up (ITT) — Total recurrences
- 17
Recurrence by tumour stage and nodal status (overall)
- pT3 or pT3a
- four [9%] of 46
- pT1 or pT2
- 13 [3%] of 458
- N1a
- six [13%] of 47
- N0 or Nx
- 11 [2%] of 457
- Rates similar among those who did not receive ablation
Safety
- Fatigue, no ablation vs ablation
- 63 [25%] of 249 vs 65 [28%] of 231
- Lethargy, no ablation vs ablation
- 34 [14%] vs 32 [14%]
- Dry mouth, no ablation vs ablation
- 24 [10%] vs 21 [9%]
- Treatment-related deaths
- 0
- Adverse events similar between groups
- Per-protocol population
Original publication
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. Published 18 June 2025. doi:10.
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