A population-based age-period-cohort study of colorectal cancer incidence comparing Asia against the West.

BACKGROUND: Colorectal cancer (CRC) is the third most common cancer worldwide but incidence varied widely. Despite the role of genetics, CRC is also sensitive to macro-environmental factors. Few studies have ever compared across different countries/regions to suggest possible macro-environmental risk factors of CRC. We estimated the effects of age, period and cohort on the changes of incidence of colorectal cancer across different countries/regions.

METHODS: Poisson regression age-period-cohort (APC) models were conducted to estimate the age, period and cohorts effects on CRC incidence across the West (i.e., the UK, the US and Australia) and Asia (i.e. Japan, Hong Kong, Shanghai, Singapore and India). We maximized the length of the study period according to each country's data availability.

RESULTS: Western populations show upward inflections for their 1950s-1960s cohorts, while Asian populations (except India) show downward inflections for their 1950s cohorts. Japanese population also shows upward inflections for its 1960s cohorts, similar to the Western populations. There are apparent upward inflections towards the more recent cohorts for Hong Kong, Shanghai and Singapore; nevertheless, the confidence intervals are wider towards the more recent cohorts.

CONCLUSION: Our findings imply an increasing risk of CRC in both Western and Asian populations as their younger cohorts reach older ages. These findings are consistent with the life course argument that macro-environmental changes associated with socio-economic development have specific effects that extend over the life course. Actions that pertain to altering lifestyle-related exposures over the life course are of great importance in combating young CRC risks in the future.