Trends in reported incidences of gastric cancer by tumour location, from 1975 to 1989 in Japan

BACKGROUND: This study was performed to estimate the incidence of gastric cancer by tumour location and to clarify whether the relative and absolute rates of gastric cancer in Japan changed between 1975 and 1989. METHODS: The stomach was anatomically divided into the upper, middle, and lower thirds. Age- and sex-specific incidences by tumour location were estimated by multiplying the age- and sex-specific national incidences of gastric cancer by the corresponding proportions of tumour location. We studied 171 721 cases of gastric cancer from the Gastric Cancer Registry of Japan. RESULTS: Over 15 years, the proportion of tumours in the upper third of the stomach increased in men but did not change much in women. The proportion of tumours in the middle third of the stomach increased among both men and women while the proportion of tumours in the lower third of the stomach decreased among both men and women. The incidence of tumours in the upper third of the stomach showed an increasing trend among elderly men and women but not among young ones. The incidence of tumours in the lower third of the stomach decreased significantly among men and women of most age groups. CONCLUSIONS: The present study added evidence of disparate trends in the incidence of gastric cancer by tumour location. The separate epidemiological features may indicate different aetiologies as well as changes in the degree of influence of these aetiologies.