Long-term Trends in Primary Sites of Gastric Adenocarcinoma in Japan and the United States

Background: The incidence and characteristics of gastric cancer have been shown to vary widely across Western and Eastern countries. Our study had two aims: to evaluate long-term trends in gastric adenocarcinoma in Japan over a period of 70 years, and to anticipate the future of gastric cancer in Japan, through comparison with data from the United States. Methods: Japanese patient data for 19,306 incident cases of gastric adenocarcinoma from 1946 - 2014 were collected from the Gastric Cancer Database at the Cancer Institute Hospital, Tokyo, Japan (CIH-GCDB). U.S. patient data for 78,625 incident cases of gastric cancer from 1973 - 2012 were obtained from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database. Changes over time in patient and tumor characteristics were investigated in these two cohorts. Results: There was a marked reduction of cancer incidence in the lower third of the stomach in the CIH-GCDB; over 70% to around 30%. The incidence in the upper third has been increasing steadily over time; 3% to 19%, although the number of cardia tumors has not changed. An increase in elderly and obese patients was also noted. In the U.S. population, there was a significant difference in the primary site across races. A notable overall increase in cardia cancer was evident in the Western population during the study period, with no similar change evident in the Japanese population over the last 15 years. In the East Asian population, the proportional frequency of tumors in the cardia was lower and that of tumors in the pyloric antrum was higher. Conclusion: In Japan, cancer in the antrum or pylorus of the stomach has been declining, whereas cancer in the body has been increasing. Unlike the Western population in the United States, adenocarcinoma of esophago-gastric junction is not increasing in Japan.