Five-year follow-up of patients with low-risk papillary thyroid cancer treated without postoperative radioiodine: prospective study by the Finnish Thyroid Cancer Group.

[BACKGROUND AND PURPOSE] The purpose of this study was to evaluate the safety of omitting radioiodine (RAI) ablation in low-risk papillary thyroid cancer.

[PATIENTS AND METHODS] All five university hospitals in Finland consecutively and prospectively enrolled patients in the study with the following inclusion criteria: age 18 or over, papillary unifocal, intrathyroidal cancer 11-20 mm operated with a thyroidectomy, and no lymph node metastases. All patients were initially offered a follow-up without RAI. The patients who did not receive postoperative RAI were included in the RAILESS group. Those who preferred to have RAI and those who received RAI due to elevated thyroglobulin (TG) or thyroglobulin antibodies (TGAb) formed the RAIRINN group. Thyroglobulin and TGAb levels were monitored 4-8 weeks postoperatively in the RAILESS group. All patients were subsequently monitored every 3 months for the first year and then annually for 5 years, with a neck ultrasound. Radioiodine was administered if TG surpassed 2 ug/L or TGAb exceeded 40 kU/L in two consecutive measurements. An event was defined as a structural recurrence or a biochemical abnormality resulting in RAI treatment. The primary endpoint was the amount of patients who remained event-free during a 5-year follow-up.

[RESULTS] Fifty-three of 60 patients enrolled were assigned to the RAILESS and 5 to the RAIRINN group. In the RAILESS group, 96% (51/53) remained event-free throughout 5 years, while 4% (2/53) required RAI due to increased TG or TGAb levels. In the RAIRINN group, one patient (1/7 or 14%) developed a metastatic disease.

[INTERPRETATION] Our findings provide additional evidence for safely omitting postoperative RAI in low-risk papillary thyroid cancer.