A proposal for a novel and simple TNM staging for gastric cancer.

Abstract

21 Background: Current TNM staging system for gastric cancer has controversies regarding N classification. We aimed to develop a simple and novel TNM staging system for gastric cancer by re-grouping N classification. Methods: We retrospectively reviewed 14260 patients treated for gastric cancer. To develop simple combinations of TNM staging with similar weighted value between T and N classification, N classification was restructured with different cutoffs. The optimal cutoffs for the number of metastatic lymph node which maximize the x2 statistic of log-rank test for survival differences among patients were selected. C-statistic was used to compare the discriminating performance of the proposed N classification with the current N classification in the TNM staging system. We performed validation with 2 external datasets from a hospital in Korea (n = 1500) and SEER (n = 11324). Results: We identified the new cutoffs of N classification as 1~4, 5~10, 11~24, and 25 or more for N1, N2, N3a, and N3b, respectively. We found survival of the new N3b classification was similar to M1, regardless of T classification. Thus, we stratified these groups of N3b and M1 disease as stage IV, simultaneously. Our new TNM staging had similar weighted value between T and N classification resulting in simple combinations. (Table) Survival curves of subgroups in the new TNM staging had higher x2 value than current staging system (x2: 8239 vs. 7023, respectively) and homogeneity among subgroups in the same stage increased. However, C-statistics (0.801, 95%CI: 0.795, 0.807) of new model showed similar discrimination power than that (0.797, 95%CI: 0.791, 0.803) in 7th TNM staging system. C-statistics were also similar in other hospital in Korea (0.805 vs. 0.802, respectively) and SEER database (0.709 vs. 0.706, respectively). Conclusions: This novel staging system by recalculating cut-offs of N classification provides exceptionally simple and practical way to stratify substages in TNM staging for gastric cancer. [Table: see text]