Lymph node ratio is inferior to pN-stage in predicting outcome in colon cancer patients with high numbers of analyzed lymph nodes

BACKGROUND: The lymph node ratio (LNR), i.e. the number of positive lymph nodes (LN) divided by the total number of analyzed LN, has been described as a strong outcome predictor in node-positive colon cancer patients. However, most published analyses are constrained by relatively low numbers of analyzed LN. Therefore, the objective of the present study was to evaluate the prognostic impact of LNR in colon cancer patients with high numbers of analyzed LN. METHODS: One hundred sixty-six colon cancer patients underwent open colon resection. All node-positive patients were analyzed for this study. The number of analyzed LN, of positive LN, the disease-free (DFS) and overall survival (OS) time were prospectively recorded. Patients were dichotomously allocated to a high or a low LNR-group, respectively, with the median LNR (0.125) as a cut-off value. Median follow-up was 34.3 months. RESULTS: Fifty-eight patients (34.9%) were node-positive. The median number of analyzed LN was 23 (range 8–54). DFS and OS were significantly shorter in pN2 vs pN1 patients (p < 0.001, and p = 0.001, respectively), and in LNR high vs low patients (p = 0.032, and p = 0.034, respectively). pN2 (vs pN1) disease showed hazard ratios (HR) of 6.2 (p < 0.001), and 6.8 (p < 0.005; for DFS and OS, respectively), while LNR high (vs low) showed HR of 3.0 (p =0.041), and 4.5 (p = 0.054). CONCLUSIONS: LNR is a reasonable outcome predictor in node-positive colon cancer patients. However, LNR is inferior to pN-stage in predicting survival in patients with high number of harvested lymph nodes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12893-018-0417-0) contains supplementary material, which is available to authorized users.