Prognostic implication of metastatic lymph node ratio in node-positive rectal cancer

PURPOSE: The aim of this study was to evaluate the prognostic significance of the ratio between metastatic and examined lymph nodes (LNs) in patients with stage III rectal cancer. METHODS: A review was made of 175 (male, 98) patients with stage III rectal cancer of R0 resection. LN disease was stratified both by the American Joint Committee on Cancer/International Union Against Cancer nodal classification (pN) and by quartiles of the lymph node ratio (LNR). Disease-free survivals (DFS) were made using Kaplan-Meier curves and assessed by the log rank test and multivariate analysis was performed using the Cox proportional hazards model. RESULTS: Patients ranged in age from 29 to 83 (median, 60) years with median follow-up of 47 months (range, 13 to 181 months). months. There was a significant correlation between the number of metastatic LNs and the LNR (r = 0.8681, P < 0.0001). Cut-off points of LNR quartiles best to separate patients with regard to 5-year DFS were between quartile 2 and 3, and between 3 and 4 (LNR1, 2, and 3); the 5-year DFS according to such stratification was 89.6%, 55.8%, and 18.2% in LNR1, 2, and 3, respectively (P < 0.0001). Cox model identified the LNR as the most significant independent prognostic covariate; LNR2 showed 3.6 times (95% confidence interval [CI], 1.682 to 7.584; P = 0.0009) and LNR3, 18.7 times (95% CI, 6.872 to 50.664; P < 0.0001) more risky than LNR1. CONCLUSION: This study suggests that ratio-based LN staging, which reflects the number of LNs examined and the quality of LN dissection, is a simple and reliable system for prognostic LN stratification in patients with stage III rectal cancer.