OBJECTIVES: Colorectal cancer (CRC) incurs a significant burden of disease globally. Organized CRC screening programs have been widely implemented for early detection and prevention. To understand the public health impact of these programs, quantitative evidence on changes in age-specific population incidences is fundamental. We aimed to provide such evidence by exploiting a natural experiment in Sweden, where two out of the 21 regions (comprising nearly 20% of the Swedish population) have offered organized screening since 2008.

METHODS: Using registry data on diagnosed CRC cases and socio-demographics for all regions in Sweden over the period 1970–2021, Bayesian structural time series modeling and difference-in-differences were applied to analyze the impact of screening on age-specific population incidences over time (CRC cases per 100.000 persons/year).

RESULTS: After successively inviting birth-year cohorts aged 60-69 years for stool-based testing, the incidence rate in the 70–74-year age group decreased significantly over time, with an average reduction of -44·40 (95% CI -58·15 to -31·31) from 2011 to 2019. In the overall population aged 60–74 years, there was a net incidence decrease of -7·99 (95% CI -13·85 to -2·39) since the initiation of organized screening in the intervention regions, 2008–2019.

CONCLUSIONS: Organized CRC screening for 60–69-year-olds generated a change in age-specific incidence patterns with a long-lasting incidence decrease in the 70–74-year-old population, implying a reduction in the excess mortality and burden of the disease.