Time trends of esophageal cancer in Hong Kong: age, period and birth cohort analyses.

This study was to examine the time trend of the incidence rates of esophageal cancer during the period 1979-2003 in Hong Kong and to identify the effects of year of diagnosis (period) and year of birth (cohort) on the observed time trends using regression models. Cancer incidence data were obtained from Hong Kong Cancer Registry and population data were from the Census and Statistics Department. Age-standardized incidence rates were computed by the direct method using the World population of 1966. Annual percentage change (APC) in incidence rate was calculated using nonlinear regression. Period and cohort effects were assessed using 2 separate Poisson regression models after adjusting for age. During the period 1979-2003, a steady decrease in the age-standardized incidence rate was observed for both males (APC = -3.38%, 95% confidence interval [CI]: -2.89%, -3.86%) and females (APC = -3.92%, 95% CI: -3.15%, -4.69%). The incidence rates were consistently higher among males than females. After the adjustment for age and with the period 1989-1993 or birth cohort of 1934-1938 as reference, the relative risk of more recent periods or birth cohorts significantly decreased. The age-cohort model provided a better description of the data than the age-period model. Given reasonable latency between exposures and esophageal cancer incidence, the declining birth cohort effects in the recent generations were in line with the increased intakes of fresh vegetables and decreased consumptions of alcohol drinking, tobacco smoking, and preserved foods observed in population, thus supported their importance in influencing the burden of esophageal cancer.