Lymph Node Ratio as a Prognostic Determinant Following Neoadjuvant Chemoradiation and Rectal Cancer Surgery

Abstract

Purpose. The purpose of this retrospective study was to compare the lymph node ratios (LNRs) of patients with rectal cancer who underwent neoadjuvant chemoradiation followed by total mesorectal excision (TME) in order to examine the applicability of this ratio as an indicator for the prognosis of rectal cancer.Methods. Lymph node ratio refers to the number of positive lymph nodes divided by the total number of lymph nodes within a given sample. Patients were categorized into three groups: LNR=0, 0＜LNR≤0.125, and LNR＞0.125. Differences in demographic distributions and clinical characteristics among the groups were detected using the Kruskal-Wallis test for continuous variables as well as the Chi-square test or Fisher's exact test for categorical variables. Survival curves were constructed according to the Kaplan-Meier method using the log-rank test to detect the difference between three LNR groups. Cox's proportional hazard regression model was used to calculate crude and adjusted hazard ratios (HR), with 95% confidence intervals (CIs), regarding the influence of LNR and other prognostic factors on overall survival (OS) and disease-free survival (DFS), respectively. Statistical analysis was performed using SAS software version 9.2 (SAS Institute Inc., Cary, NC). Two-tailed p＜0.05 indicated statistical significance. Results. The distributions of pT stage (p=0.019), pN stage (p＜0.001), and pTNM stage (p＜0.001) differed significantly among the three LNR groups. Cases of more advanced stages of the disease were observed in groups with higher LNR. Patients with higher LNR had a greater number of lymph nodes examined (p=0.002), higher number of positive lymph nodes (p＜0.001), and a greater proportion of positive LVSI (p＜0.001). The DFS curves among the three LNR groups differed significantly (log-rank test, p＜0.0001); however, the OS curves did not reach significance (p=0.065). Survival curves indicated that patients with LNR＞0.125 had a worse prognosis than patients in the other two groups. However, the differences in OS and DFS between groups with LNR=0 and 0＜LNR≤0.125 were not significant.Conclusion. This study indicates that LNR is an important prognostic indicator of disease-free survival among patients who undergo neoadjuvant chemoradiation followed by TME for rectal cancer.