Critical prognostic value of the log odds of negative lymph nodes/tumor size in rectal cancer patients

BACKGROUND: The number of negative lymph nodes (NLNs) and tumor size are associated with prognosis in rectal cancer patients undergoing surgical resection. However, little is known about the prognostic significance of the NLN count after adjusting for tumor size. AIM: To assess the prognostic impact of the log odds of NLN/tumor size (LONS) in rectal cancer patients. METHODS: Data of patients with stage I–III rectal cancer were extracted from the Surveillance, Epidemiology, and End Results Program database. These patients were randomly divided into a training cohort and a validation cohort. Univariate and multivariate Cox regression analyses were used to determine the prognostic value of the LONS. The optimal cutoff values of LONS were calculated using the "X-tile" program. Stratified analysis of the effect of LONS on cancer-specific survival (CSS) and overall survival (OS) were performed. The Kaplan-Meier method with the log-rank test was used to plot the survival curve and compare the survival data among the different groups. RESULTS: In all, 41080 patients who met the inclusion criteria were randomly divided into a training cohort (n = 28775, 70%) and a validation cohort (n = 12325, 30%). Univariate and multivariate analyses identified the continuous variable LONS as an independent prognostic factor for CSS [training cohort: Hazard ratio (HR) = 0.47, 95% confidence interval (CI): 0.44–0.51, P < 0.001; validation cohort: HR = 0.46, 95%CI: 0.41-0.52, P < 0.001] and OS (training cohort: HR = 0.53, 95%CI: 0.49-0.56, P < 0.001; validation cohort: HR = 0.52, 95%CI: 0.42-0.52, P < 0.001). The X-tile program indicated that the difference in CSS was the most significant for LONS of -0.8, and the cutoff value of -0.4 can further distinguish patients with a better prognosis in the high LONS group. Stratified analysis of the effect of the categorical variable LONS on CSS and OS revealed that LONS was also an independent predictor, independent of pN stage, pT stage, tumor-node-metastasis stage, site, age, sex, the number of examined lymph nodes, race, preoperative radiotherapy and carcinoembryonic antigen level. CONCLUSION: LONS is associated with improved survival of rectal cancer patients independent of other clinicopathological factors.