Superiority of the 8th edition of the TNM staging system for predicting overall survival in gastric cancer: Comparative analysis of the 7th and 8th editions in a monoinstitutional cohort

Abstract

The present study was performed to evaluate the predictive capacity of the 8th edition vs. the 7th edition of the American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) staging system for overall survival (OS) of patients with gastric cancer. Data of eligible patients with gastric cancer in our institution between June 2004 and June 2014 were retrospectively reviewed. A total of 1,506 patients were followed up to July 2016, among whom 1,484 patients with complete stage information were included in the TNM staging analysis. A total of 339 (22.8%) patients presented stage migration, including 325 (21.9%) migrating to a lower tier and 14 (0.9%) to a higher tier. All patients with stage migration to a lower tier were in stage III, including 177 (54.5%) patients migrating from stage IIIB to IIIA, and 148 (45.5%) from stage IIIC to IIIB. Patients migrating from IIIB to IIIA yielded a median OS time and 5-year OS rate closer to those remaining in stage IIIA. Similarly, patients migrating from IIIC to IIIB yielded a median OS time and 5-year OS rate closer to those remaining in stage IIIB. The 7th edition of the staging system exhibited prognostic discrepancy in discriminating stage IIIA from IIIB on survival curves, which was improved in the 8th edition. The 8th edition had a better predictive capability of survival, as evidenced by a smaller value of -2log likelihood in the Cox proportional regression model (7th edition 4738.859 vs. 8th edition 4736.683). Therefore, the present study demonstrated that the 8th edition of the AJCC TNM staging system is superior to the 7th edition in predicting the OS of patients with gastric cancer.

Keywords: 8th edition; American Joint Committee on Cancer; gastric cancer; survival; tumor-node-metastasis classification.

Figure 1.

Kaplan-Meier survival curves for patients stratified by N category with (A) undivided N3 and (B) subdivided N3 into N3a and N3b. The log-rank test for trend showed significantly decreased survival in patients with advanced N stage by both N classifications (both P<0.001), but the 8th TNM classification exhibited a better monotonicity of gradient compared with the 7th TNM classification (χ² for log-rank trend test, 311.783 vs. 297.588).

Figure 2.

Kaplan-Meier survival curves for patients based on (A) the 7th AJCC staging system and (B) the 8th AJCC staging system. The 7th edition staging system exhibited insufficient prognostic discrepancy for discriminating stage IIIA from IIIB on survival curves (P=0.260), which was improved in the 8th edition (P<0.001). AJCC, American Joint Committee on Cancer.