Timing of recurrence in papillary thyroid carcinoma: Analysis of recurrent cases after initial surgery

OBJECTIVE: Papillary thyroid carcinoma (PTC) generally has an excellent prognosis; however, recurrence may occur over a wide range of postoperative periods, and factors associated with the timing of recurrence remain unclear. Previous studies have evaluated early or late recurrence using predefined time points or specific recurrence patterns. We aimed to evaluate the association between clinicopathological and treatment-related factors and the timing of recurrence across the entire postoperative period. METHODS: We retrospectively analyzed 69 patients with recurrent PTC among 677 patients who underwent initial surgery. Recurrence timing was defined as the postoperative month (POM), calculated from the date of initial surgery to the date when recurrence was first identified. We evaluated the distribution of POM and compared recurrence timing across clinicopathological and treatment-related subgroups. Cumulative recurrence curves were constructed, and differences in POM were assessed using the Mann-Whitney U test or Kruskal-Wallis test, as appropriate. Multivariable linear regression analysis was also performed to identify factors independently associated with recurrence timing. RESULTS: The median POM was 34 months (IQR, 13-73), with 71% of recurrences occurring within POM 60 (5 years), 25% between POM 60 and 120 (5-10 years), and 4.3% after POM 120 (>10 years). Most clinicopathological and treatment-related factors, including T classification, N classification, recurrence site, recurrence risk group, age, extent of thyroidectomy, and radioactive iodine treatment, were not significantly associated with recurrence timing. In contrast, multifocal tumors were associated with earlier recurrence than solitary tumors (median POM, 20 vs. 48 months; p = 0.015). Multivariable linear regression analysis also demonstrated that tumor multifocality was independently associated with a shorter time to recurrence. CONCLUSION: Recurrence timing in PTC was highly variable and was difficult to predict using conventional clinicopathological and treatment-related factors. Tumor multifocality was associated with earlier recurrence, suggesting that patients with multifocal tumor may benefit from closer surveillance during the early postoperative period. However, late recurrence also occurred, including more than 10 years after surgery, indicating that long-term surveillance remains important. These findings may support a risk-adapted approach to postoperative surveillance, although the optimal intensity and duration of follow-up require further investigation.