Prognostic Significance of the Number of Metastatic Lymph Nodes to Stratify the Risk of Recurrence

Prophylactic dissection facilitates identification of central lymph node (LN) metastasis in patients with papillary thyroid cancer (PTC). Because most staging systems do not stratify risks by the number of LN metastases, postoperative treatments vary among different institutions. Therefore we investigated the significance of number of LN metastases in risk stratification for recurrence in PTC. A retrospective review was performed for 3,305 patients who had undergone thyroidectomy at Ajou University Hospital. A total of 2,462 patients (73.5 %) underwent total thyroidectomy, and another 3,152 (94.1 %) underwent central LN dissection. Lateral cervical LN dissection had been performed in 420 patients (12.5 %). There were 115 patients with recurrence (3.4 %). Recurrence-free rates were 94.6 % at 5 years and 89.4 % at 10 years. On univariate analysis, prognostic factors for recurrence were extent of thyroidectomy, tumor size, capsular invasion, T stage, N stage, number of LN metastasis, TNM stage, and radioactive iodine (RAI) therapy. On multivariate analysis, number of LN metastasis and N stage were significant prognostic factors for recurrence. Recurrence-free rate was significantly different between patients with 0-1 LN and those with 2 or more LN. Number of metastatic LN was a significant prognostic factor, in addition to the N stage. Therefore, number of metastatic LN must be considered for postoperative staging system to tailor treatment and follow-up recommendations. In addition, patients with a parts per thousand yen2 metastatic LN may benefit from total thyroidectomy and RAI therapy with postoperative follow-up with serum thyroglobulin.