TIME TREND AND AGE-PERIOD-COHORT EFFECTS ON GASTRIC-CANCER INCIDENCE IN ZARAGOZA AND NAVARRE, SPAIN

Study objective-To describe time trends in gastric cancer incidence in Zaragoza and Navarre, and to investigate time period and birth cohort as determinants of such trends. Design-Cases from two registries were grouped into five year intervals and the following were calculated: a ge specific and sex specific incidence rates, age adjusted incidence r ates, cumulative rates, and the male to female ratio. Log linear model s including age, period of diagnosis, and birth cohort were fitted. Se tting-The Zaragoza Cancer Registry covers the province of Zaragoza, wh ich has a population of 824 776 (403 755 men and 421 021 women). The N avarre Cancer Registry covers the province of Navarre which has 512 51 2 inhabitants (254 786 men and 257 726 women). In both cases populatio n figures were based on the 1986 census. Patients-These comprised inci dent cases of gastric cancer reported to the Zaragoza Cancer Registry in 1963-87 and to the Navarre Cancer Registry in 1973-87.Main results- Navarre registered higher adjusted and cumulative rates than Zaragoza for both sexes. In both provinces, there were relative declines in the rates for men and women of 3% and 4% respectively per year. In Zarago za, the risk of developing stomach cancer fell in generations born bet ween 1888 and 1933, and rose in subsequent birth cohorts in both sexes , while in Navarre the cohort effect showed an approximately linear de crease in risk for both sexes. Both provinces recorded increases in ri sk associated with cohorts born between 1933 and 1943. Conclusions-The incidence rates of gastric cancer fell in both Zaragoza and Navarre. The reason for the greater incidence of gastric cancer in Navarre rema ins unknown. Trends in rates seem to be mainly linked to birth cohort. Increases in risk in generations born after 1933 may be ascribable to nutritional deficiencies in the early years of life.