Can Lymph Node Ratio Take the Place of pN Categories in the UICC/AJCC TNM Classification System for Colorectal Cancer?

Lymph node ratio (LNR) has been reported to represent a powerful independent prognostic value in some malignancies. The significance of LNR in colorectal cancer is still under debate. A total of 505 patients with stage III colorectal cancer were reviewed. Using running log-rank statistics, we calculated the best cutoff values for LNRs and proposed a novel rN category: rN1, 0% < LNR a parts per thousand currency sign 35%; rN2, 35% < LNR a parts per thousand currency sign 69%; and rN3, LNR > 69%. A Spearman's correlation coefficient test was used to assess the correlation between the number of retrieved nodes and the number of metastatic nodes, as well as the number of retrieved nodes and the LNRs. Univariate and two-step multivariate analyses were performed, respectively, to identify the significant prognostic clinicopathologic factors. The 5-year overall survival rate decreased significantly with increasing LNRs: rN(1) = 61% survival rate, rN(2) = 30.3% survival rate, and rN(3) = 11.2% survival rate (P < 0.001). Univariate and two-step multivariate analyses identified the rN category as a significant prognostic factor no matter whether the minimum number of LNs retrieved was met. There was a significant prognostic difference among different rN categories for any pN category, but no apparent prognostic difference was seen between different pN categories in any rN category. Moreover, marked heterogeneity could be seen within IIIa-c substages when survival was compared among rN(1-3) categories but not between pN(1-2) categories. rN categories have more potential for predicting patient outcomes and are superior to the UICC/AJCC pN categories. We recommend rN categories for prognostic assessment and rN categories should be reported routinely in histopathological reports.