IoN

IoN, trial NCT01398085 sponsored by Cancer Research UK and UCL and published in the Lancet in 2025, is the UK trial confirming that low-risk differentiated thyroid cancer patients can safely avoid radioactive iodine after thyroidectomy. It randomised 504 patients with pT1 to T2, node-negative tumours without adverse features to no radioiodine or radioiodine ablation and met its non-inferiority endpoint on recurrence-free status at five years, extending the ESTIMABL2 finding to pT2 tumours. OnCo links it to thyroid cancer, radioiodine therapy, radioactive iodine, the low-risk thyroid cancer term and Cancer Research UK, and it replicates ESTIMABL2. Guideline bodies now recommend against routine ablation in this group, and whether patients and clinicians accept doing less is the practical question that remains.