Adjustment of N stages of gastric cancer by the ratio between the metastatic and examined lymph nodes

Background: The present study attempted to determine whether N stage could be adjusted for the differences in survival rates based on the ratio between the examined and metastatic lymph nodes (LN ratio). Methods: Five hundred and twenty-nine patients with both >15 lymph nodes examined and ≥ N1 after R0 resection were enrolled in the present study. To determine the cutoff LN ratio, the ratios at each N stage were compared at intervals of 10% with the log-rank test of Kaplan-Meier estimates of the survival curves. Results: The 5-year survival rate of patients with N1 was 71.7%. Those of N2 patients with LN ratio of <60% (n = 116) and ≥60% (n = 3) were 37.0% and 0%, respectively. Those of N3 patients with LN ratio of <30% (n = 32), between 30% and 60% (n = 67), and ≥60% (n = 26) were 31.0%, 16.3%, and 0%, respectively. Thus, adjusted N2 was obtained from the sum of N2 < 60% and N3 < 30%. N3 with an LN ratio between 30% and 60% was regarded as adjusted N3. N2 and N3 patients with an LN ratio of ≥60% were regarded as adjusted T4. The 5-year survival rate in patients with adjusted N2, N3, and N4 were 35.7%, 16.3%, and 0%, respectively. Multivariate analysis showed adjusted N stage and tumor depth were significant independent prognostic factors. Conclusions: The results of this study suggest that, since stage migration can be induced in the N staging system, such stage migration can be adjusted by the LN ratio based on the survival rate.