Determinant Factors on Differences in Survival for Gastric Cancer between the US and Japan Using Nationwide Databases: The Impact of Number of Lymph Nodes Examined

Background: Although the incidence and mortality have decreased, gastric cancer (GC) is still a public health issue globally. An international collaborative study reported much higher survival in Korea and Japan than other countries, including the US. We examined the determinant factors of the high survival in Japan, compared with the US.   Methods: We analysed data on 78,648 cases from the nationwide GC registration project, the Japanese Gastric Cancer Association (JGCA), from 2004-2007 and compared them with 16,722 GC cases from the Surveillance, Epidemiology, and End Results Program (SEER), a US population-based cancer registry data from 2004-2010. We estimated five-year relative survival and applied a multivariate excess hazard model to compare the two countries. We considered the effect of number of lymph nodes (LNs) examined on differences in survival. Findings: Five-year relative survival in Japan was 81.0%, compared with 45.0% in the US. After controlling for confounding factors, we still observed significantly higher survival in Japan. The effect of number of LNs examined showed different trends according to TNM-N categories. N0 and N1 patients showed much wider gaps between the two countries. Among N2 patients, a higher number of LNs examined showed better survival in both countries. Among N3 patients, the relationship between number of LNs examined and differences in survival between the two countries disappeared.   Interpretation: The wide differences in gastric cancer survival between Japan and US can be largely explained by differences in the stage at diagnosis, which were related to early detection in Japan, mainly due to the screening system and greater awareness of gastric cancer. Stage migration, which is related to differences in the number of retrieved and examined LNs, also helps explain the wide gap in gastric cancer survival between the two countries.   Funding Statement: Ministry of Health, Labour and Welfare, Japan   Declaration of Interests: The authors have no conflict of interest.