Importance: Population-based colorectal cancer (CRC) screening programs are implemented worldwide, but there are difficulties evaluating their effectiveness. The magnitude of routine CRC screening effectiveness regarding cancer-specific mortality is unclear.
Objective: To evaluate cancer-specific mortality associated with early vs late or no invitation for routine CRC screening using fecal occult blood testing.
Design, setting, and participants: This prospective cohort study was performed in the region of Stockholm-Gotland, Sweden, between January 1, 2008, and December 31, 2021. All individuals of the target population of screening born from 1938 to 1954 were included. Data were analyzed from December 12, 2022, to June 25, 2023.
Exposures: Individuals were invited early (2008-2012), late (2013-2015), or not at all to screening with biennial guaiac-based fecal occult blood test. The early invitation group was considered the exposure group and the late or no invitation group was considered the control group.
Main outcomes and measures: The main outcome was cancer-specific mortality, defined as CRC registered in the Cancer Register with CRC as underlying cause of death in the Cause of Death Register. Excess mortality was calculated as all-cause deaths among the individuals with CRC subtracted from the expected number of deaths had they not had CRC. Poisson regression analysis based on deaths and person-years was used to estimated mortality rate ratio (RR) with 95% CIs, adjusted for follow-up years and attained age.
Results: In total, 379 448 individuals (193 436 [51.0%] female) were invited for CRC screening, including 203 670 individuals in the exposure group and 175 778 in the control group. The mean screening participation rate was 63.3%, and there was a maximum of 14 years follow-up. There were 834 CRC deaths in 2 190 589 person-years in the exposure group, compared with 889 CRC deaths in 2 249 939 person-years in the control group. Individuals who underwent early CRC screening had reduced adjusted risk of CRC mortality (RR, 0.86; 95% CI, 0.78-0.95) and excess mortality (RR, 0.84; 95% CI, 0.75-0.93).
Conclusions and relevance: This prospective cohort study of routine screening with fecal occult blood testing found a 14% decrease in CRC mortality associated with screening. The true association of screening with reduced mortality is expected to be higher due to some coexistence of testing in the control group and CRC deaths diagnosed more than 2 years after screening.