Proposal for a New TNM Stage based on the 7(th) and 8(th) American Joint Committee on Cancer pTNM Staging Classification for Gastric Cancer

Background: The 8(th) edition of the American Joint Committee on Cancer (AJCC) staging system for gastric cancer incorporated several new changes. We aimed to assess the comparative prognostic values of the 7(th) and 8(th) AJCC pTNM staging systems in patients with gastric cancer (GC), and accordingly, to put forward a refined staging classification. Methods: The SEER database was queried to identify GC patients between 2004 and 2009. GC patients from Sun Yat-sen University Cancer Center (SYSUCC) were used as external validation data. The Kaplan-Meier method and Cox proportional hazards regression models were used to analyze cause-specific survival (CSS). The prognostic performance of different staging schemes was assessed using the concordance index (c-index), Akaike's information criterion (AIC), and likelihood ratio χ(2) test. Results: In the SEER cohort, stage migration occurred in 8.74% of patients. Survival analysis showed that it was better to treat T4bN0M0 + T4aN2M0 as stage IIIB and T4bN3bM0 as stage IV. Based on this, we established a new staging system which exhibited a superior c-index (0.7501) to the 7(th) and 8(th) AJCC staging systems (0.7498 and 0.7500, respectively). The new staging system also outperformed the 7(th) and 8(th) AJCC staging systems in terms of AIC and the likelihood ratio χ(2) test. The predictive superiority of the new staging system remained valid in the SYSUCC database. Conclusions: We demonstrated that some stage modifications in the 8(th) AJCC pathologic staging were unnecessary. Therefore we established a new staging system, which was superior to the 7(th) and 8(th) staging systems.