Lymph Node Ratio as a Quality and Prognostic Indicator in Stage III Colon Cancer

Background: The presence and number of nodal metastasis significantly impact colon cancer prognosis. Similarly, the number of resected/evaluated nodes impacts staging accuracy. This ratio of metastatic to examined nodes or lymph node ratio (LNR) may have independent prognostic value in colon carcinoma. Purpose: To evaluate the impact of LNR on overall survival in colon cancer patients with fewer than 12 or 12 examined nodes or more. Methods: Patients (n = 36,712) with node-positive nonmetastatic colon cancer diagnosed between 1992 and 2004 were identified from the Surveillance, Epidemiology, and End Results database and stratified according to LNR and number of nodes examined. Survival was estimated by Kaplan-Meier method, and differences analyzed by log-rank test. A Cox proportional hazards model was used for multivariate analysis. Results: Patients with fewer than 12 nodes were older and male and had lower primary tumor stage, grade, and N stage (P < 0.01). Survival appeared greater with 12 total nodes examined or more (median 53 vs. 66 months, P < 0.001). Within each LNR stratum, survival with 12 nodes or more was improved for those with less than 10% of nodes positive for cancer, but was worse with higher LNRs (P < 0.01). Lymph node ratio was significantly associated with survival independent of total nodes (HR 1.24-5.12, P < 0.001). Other significant factors included age, race, tumor grade, stage, location, and N stage. Conclusion: Metastatic LNR independently estimates survival in Stage III colon cancer, irrespective of number of nodes examined. However, statistically significant differences in each LNR stratum between those with resection of fewer than 12 or 12 nodes or more would indicate that a 12-node minimum may still be necessary for accurate staging.