Validation of the 8th Edition of the AJCC TNM Staging System for Gastric Cancer using the National Cancer Database

Background: The 8th edition AJCC gastric cancer staging manual was refined using Japanese and Korean data from the International Gastric Cancer Association (IGCA). This study evaluated the eighth edition’s validity for U.S. populations. Methods: National Cancer Database (NCDB) was used to obtain data on gastric cancer patients diagnosed from 2004 to 2008 who underwent surgery and to examine differences in stage grouping and survival between AJCC 7th and 8th editions. Discrimination of models derived from NCDB and IGCA data was compared. Results: Of 12,041 patients, median age was 65, 57.6% were male, median lymph nodes retrieved was 2 (0–76), 30.9% underwent distal/partial gastrectomy, and 49.8% received no adjuvant treatment. The 8th edition differed in that T1–T3 disease was upstaged with N3b, T4aN3a was downstaged from IIIC to IIIB, and T4bN0 and T4aN2 were downstaged from IIIB to IIIA. These changes resulted in increased patients in IIIA (1436 in the 7th edition to 2310 in the 8th) and IIIB (1737–1896) and decreased in IIIC (2100–1067). This also resulted in lower median survival for IIIA (28.7–25.0 months), IIIB (19.6–17.4), IIIC (13.7–11.8). The concordance index for the 8th edition applied to NCDB data was 0.719 [95% confidence interval (CI) 0.703–0.734), which is comparable to that for the 8th edition developed from IGCA data (0.775, 95% CI 0.770–0.780) and the 7th edition applied to NCDB data (0.720, 95% CI 0.704–0.735). Conclusions: The 8th edition is valid for U.S. populations, showing clear separation of data with preservation of group order.