Radioactive iodine ablation does not prevent recurrences in patients with papillary thyroid microcarcinoma

Objective: Although papillary thyroid microcarcinoma (PTMC) has a favourable long-term prognosis, disease recurrence after initial treatment remains a problem and controversy exists regarding the role of radioactive iodine (RAI) ablation in PTMC. We performed this study to evaluate the effect of RAI ablation on disease recurrence in patients with PTMC. Patients and Methods Between 1994 and 2004, 2579 patients underwent thyroid surgery for thyroid cancer at Samsung Medical Center. Among these patients, 704 patients with PTMC presumed disease-free after initial treatment were followed up for disease recurrence (median, 64 months; range, 1-185 months). Patients with PTMC with microscopic extrathyroidal extension, cervical lymph node metastases or multifocality were considered to be in the intermediate-risk group for recurrence. Results: Disease recurrence was found in six patients at a median of 29 months (range, 10-70 months) after initial treatment; all six patients with recurrent tumours had received RAI treatment after total thyroidectomy. Disease-related mortality was not observed, even after recurrence. Based on a Cox regression model considering the standardized inverse probability of treatment weight (IPTW) within each propensity score stratum of patients with a similar likelihood of having received RAI ablation, the likelihood ratio for recurrence did not differ between the RAI ablation group and no RAI group (P = 0.17). When we performed a subgroup analysis considering only patients with PTMC at intermediate-risk for recurrence, RAI ablation again did not have a significant effect on recurrence (P = 0.79). Conclusions: Radioactive iodine ablation after total thyroidectomy in low- and intermediate-risk patients with PTMC did not prevent recurrent tumours. Future randomized, controlled, multicenter prospective trials involving a larger sample of patients followed-up for a longer duration are warranted to confirm our findings.