Abstract: Background and purpose: Lymph node metastasis commonly occurs in papillary thyroid carcinoma (PTC). The object of this study was to investigate the relationship between the rate of involved lymph nodes (LR) and distant metastasis (DM) in PTC, and its potential value in predicting the risk of DM. Methods: PTC patients were divided into two groups as M₀ (121 cases) and M₁ (41 cases) according to the presence of distant metastases or not. The t-text and χ² test were used to evaluate the statistical differences in basic clinicopathological features between the two groups. Multivariate analysis was used to quantify LR as an independent factor of DM. The receiver operating characteristic (ROC) curve was employed to evaluate the clinical value of LR and the number of involved lymph node (LNs) for predicting DM and optimal cut-off point respectively. The cumulative risk of distant metastasis curves according to the LR and LNs status were constructed with the Kaplan-Meier method, and the Log-rank test was used to compare these curves. Results: There were no statistical differences in age and multifocality between two groups (P>0.05), while significant differences in gender, extrathyroidal invasion and tumor size were observed. LR is an independent indicator for predicting DM (OR=1.133, P=0.000). An increase in LR was significantly associated with DM. Patients with more than 15 involved LNs had the steepest increasing pattern in the cumulative risk of DM compared with those who had less than 15 involved LN (P=0.002). Conclusion: LR may be an independent predictive marker for distant metastases in PTC, and its combination with LNs might better predict the risk of DM.

Key words: Papillary thyroid carcinoma, The rate of involved lymph nodes, The number of involved lymph nodes, Distant metastasis