Validation of the American Joint Committee on Cancer (AJCC) 8th edition stage system for gastric cancer patients: a population-based analysis

Background Our aim was to validate the American Joint Committee on Cancer (AJCC) 8th edition stage system for gastric cancer in the Western world and to compare several modifications between the 7th and 8th edition systems. Methods Eligible patients having undergone surgical resection of gastric cancer during 2004-2011 from the Surveillance, Epidemiology, and End Results (SEER) database were included in the current study. Survival differences were assessed by Kaplan-Meier curve and log-rank tests. The discriminative power of the AJCC 8th and 7th editions was compared by Harrell's concordance index (c-index). Results Patients with pN3a and pN3b presented distinct survival outcomes, especially for cases in which more than 15 lymph nodes were examined. The overall (OS) and cancer-specific survival (CSS) c-indices for the 8th edition were largely comparable with c-indices for the 7th edition throughout the cohort. Notably, the new edition improved the power of discrimination slightly in OS and CSS (c-indices: 0.717, 0.744) compared with the 7th edition (c-indices: 0.712, 0.739) for patients for whom 15 or more lymph nodes were examined. The analysis of stage migration in the new edition revealed nonhomogeneous survival outcomes in stages IIIB and IIIC. Conclusion The AJCC 8th stage system for gastric cancer performs as well as the AJCC 7th edition in the United States (USA). Importantly, when more than 15 lymph nodes are examined, the discriminatory performance of the new edition is improved.