Study summary

Skipping radioactive iodine after surgery did not raise the chance of the cancer returning

IoN trial · 504 people at 33 UK centers · Published June 2025, The Lancet

What was tested

After removal of the whole thyroid, people with low-risk thyroid cancer were assigned to radioactive iodine or no radioactive iodine, then checked with yearly neck scans and blood tests.

What they found

• After 5 years, 97.9% of people who skipped radioactive iodine and 96.3% of those who had it were free of cancer.
• Only 17 people had the cancer return across both groups over about 7 years.
• Side effects such as tiredness and dry mouth were similar in both groups.
• The authors conclude radioactive iodine can be avoided for small tumors that have not spread to lymph nodes (pT1 or pT2, N0 or Nx).

What it means

For many people with low-risk thyroid cancer, surgery alone is enough. It confirms a French trial (ESTIMABL2) that reached the same conclusion.