Marked impact of tumor location on the appropriate cutoff values and the prognostic significance of the lymph node ratio in stage III colon cancer: a multi-institutional retrospective analysis

Background The prognostic significance of lymph node ratio (LNR) is not constant among studies. Exploration of appropriate location-specific cutoffs might be necessary because the number of lymph nodes harvested is generally higher in right than in left colon cancer. We aimed to determine appropriate cutoff values of LNR in right and left colon cancer and to clarify its clinical significance. Methods The clinicopathologic data of 5463 patients with stage III colon cancer were collected. The best cutoff for LNR as a prognostic indicator for patients with right and left colon cancer was studied separately. We compared the prognostic impact between LNR and the number of lymph node metastasis using the Akaike information criterion (AIC), and evaluated the prognostic significance of LNR in each stage III subcategory. Results The best performance was noted when LNR was categorized by cutoffs of 0.16 and 0.22 for right and left colon cancer, respectively. AIC scores were better with these categorizations than with subgrouping by number of positive nodes. LNR-low right colon cancer patients showed better cancer-specific survival than LNR-high in stage IIIA (95.7% vs. 89.3%), IIIB (86.7% vs. 77.2%), and IIIC (71.2% vs. 58.7%). The same results were obtained in left colon cancer patients with stage IIIB (88.3% vs. 80.7%) and IIIC (79.8% vs. 68.4%). Conclusions We demonstrated the difference in the appropriate cutoffs of LNR between right and left colon cancer. Categorization by location-specific cutoff of LNR may be useful for risk stratification of patients with stage III cancer.