Impact of the Number of Lymph Nodes Examined on Differences in Survival for Surgically Treated Gastric Cancer Patients Between the US and Japan Using Nationwide Databases

Background: Although incidence and mortality have decreased, gastric cancer (GC) is still a public health issue globally. The international collaborative study for cancer survival using population-based cancer registry showed that the survival of GC was higher in Korea and Japan than other countries, including the United States of America (US). Aim: We examined the determinant factors of the high survival in Japan, compared with the US, with particular focus on the impact of the number of lymph nodes (LNs) examined for surgically treated patients. Methods: We obtained data on 88,447 cases from the nationwide GC registration project, the Japanese Gastric Cancer Association (JGCA), from 2004-2007. We also obtained 18,995 GC cases from US population-based cancer registry data from the Surveillance, Epidemiology, and End Results Program (SEER), diagnosed from 2004-2010. We estimated five-year relative survival and applied a multivariate excess hazard model to compare the two countries. We considered the effec...