An evaluation of lymph node yield and lymph node ratio in well-differentiated thyroid carcinoma.

It is unknown whether the number of lymph nodes harvested (lymph node yield, LNY) or the proportion of metastatic lymph nodes resected (metastatic lymph node ratio, MLNR) influence survival in well-differentiated thyroid carcinoma (WDTC). We hypothesized that overall survival in WDTC is influenced by the LNY and MLNR. We used the Surveillance, Epidemiology, and End Results database to identify all patients with primary, nonmetastatic WDTC who underwent thyroidectomy with at least one lymph node removed between 1988 and 2004. Kaplan-Meier survival curves for LNY and MLNR were compared using the log rank test. Multivariate Cox proportional hazards models included tumor and patient-specific factors. WDTC patients that met entry criteria totaled 9926. In the univariate model, LNY and MLNR had a significant impact on survival (P < 0.001). In multivariate analysis, increasing LNY was associated with poorer survival in all patients (P = 0.001) and node-negative patients (P = 0.03), but not for node-positive patients (P = 0.27). MLNR did not influence survival in node-positive patients (P = 0.84). Among patients with WDTC treated with thyroidectomy and lymphadenectomy, increasing LNY and MLNR were associated with decreased survival. The decrease in survival associated with increasing LNY, even in node-negative patients, indicates that nodal understaging is inconsequential to WDTC survival.