Abstract
IntroductionColorectal cancer (CRC) incidence among adults younger than 50 years has increased in recent decades, leading to some advocating for lowering the age to start CRC screening. Here, we estimate age-specific trends in CRC incidence in Canada and changes in risk by birth cohort. MethodsCRC incidence data from 1971 to 2021 by province, sex, and five-year age group (35−64) were obtained from the National Cancer Incidence Reporting System and the Canadian Cancer Registry. Annual percent changes in age-specific or age-adjusted incidence rates were analyzed with joinpoint regression. Birth cohort effect was estimated with age-period-cohort models and reported as cohort incidence rate ratios (IRRs) with respect to the 1947–51 cohort. ResultsCRC incidence has increased among all age groups under 50 years, with the largest relative increases occurring in the youngest age group (35–39 years). Males and females had similar incidence trends, though males under age 50 had larger increases than females. The birth cohort analysis showed that males born since 1966 have a significantly higher risk than those born at any other time. ConclusionsThese results up to 2021 confirm and update reports that CRC incidence is increasing among adults under age 50 in Canada and that the youngest birth cohorts carry the highest risk. Future studies should assess the effectiveness of CRC screening in younger populations.
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