Number of Metastatic Lymph Nodes and Ratio of Metastatic Lymph Nodes to Total Number of Retrieved Lymph Nodes Are Risk Factors for Recurrence in Patients With Clinically Node Negative Papillary Thyroid Carcinoma

OBJECTIVES: The number of metastatic lymph nodes (LNs) and the ratio between the number of metastatic LNs and the total number of retrieved LNs (the LN ratio [LNR]) have been proposed as risk factors for recurrence of papillary thyroid carcinoma (PTC). However, the significance of the number of LNs and the LNR in patients with clinically node negative PTC has not been clearly determined. The purpose of this study is to evaluate their significance. METHODS: We retrospectively analyzed 382 patients with PTC who had undergone total thyroidectomy with prophylactic central neck dissection (CND) between January 2000 and December 2010. We excluded patients with lobectomy, concurrent lateral compartment neck dissection, a follow-up period less than at least 2 years, number of harvested central LNs less than or equal to one, clinically positive LN, distant metastasis, recurrent cancer or other types of malignancy. The correlations between recurrence and various clinicopathologic characteristics including tumor size, extrathyroidal extension (ETE), stage, number of metastatic central LNs, and the LNR were investigated. RESULTS: After a mean follow-up period of 82.2±26.4 months, recurrence occurred in 14 patients (3.7%). Tumor size ≥20 mm, maximal ETE, presence of central LN metastasis, number of metastatic LNs ≥2, and LNR ≥0.31 correlated with recurrence in the univariate analysis. However, tumor size ≥20 mm, maximal ETE, number of metastatic LNs ≥2, and LNR ≥0.31 were significantly associated with recurrence in the multivariate analysis (hazard ratio=6.61, 7.17, 3.43, and 11.23, respectively). CONCLUSION: The LNR and the number of metastatic LNs are independent prognostic risk factors for recurrence in patients with clinically node negative PTC, and these factors can be used to guide postoperative adjuvant therapy and follow-up strategy after prophylactic CND.