Colorectal cancer incidence in a multi-ethnic population: Age-period-cohort analysis of trends in Singapore

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Introduction

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers worldwide, with an estimated 1.8 million incident cases reported in 2018 [1] . Population-based trends of CRC incidence have been known to vary considerably among countries and societies. Over the last few decades, CRC incidence has been gradually increasing in most of Europe [2] while other traditionally western societies (e.g. the United States) have either experienced a stabilisation or decline in rates [2] . CRC incidence rates have also been noted to have increased within developing countries including the Philippines, China, and Belarus [23] . As suggested elsewhere, it is likely that these varying CRC trends are due to sociodemographic effects, like age and birth cohort, across populations and time periods which reflect influences such as changes to diet [4] .

In the context of Singapore, CRC remains the most commonly diagnosed cancer overall [4] , accounting for 5799 (16.8%) and 4835 (13.1%) of all incident cancers diagnosed in males and females respectively from 2013 to 2017 [5] . CRC risk is known to be multifactorial, and has been attributed to a combination of both modifiable (such as diet, tobacco smoking and sedentary lifestyle) and nonmodifiable (genetically influenced family or personal history) factors [67] . While CRC screening via Singapore’s national Screen for Life programme and advances in multimodality treatment have overall resulted in CRC being detected earlier with better prognoses, the age-standardised incidence rate (ASRs) of CRC in Singapore has plateaued in recent years [5] . More significantly, statistics from the National Registry of Diseases Office (NRDO) have suggested that there may be ethnic differences in the epidemiology of CRC within the Singaporean population, a characteristic that has also been found in other multi-ethnic populations [89] .

The most contemporary analysis for Singapore has considered CRC risk from 1968 to 2002, and demonstrated sex related differences in CRC incidence rates using age-period (AP) and age-cohort (AC) models [4] . Since the most recent analysis in Singapore was over a decade ago, we aimed to provide an updated analysis of CRC incidence rates for the Singaporean population, and to apply age-period-cohort (APC) analysis to gain an understanding of CRC incidence trends in Singapore using all reported CRC cases from 1968 to 2017, focusing specifically on sex and ethnic differences.