Colorectal Cancer Mortality Following an Organized Fecal Immunochemical Test–Based Screening Program

Importance Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide. Organized screening programs using the fecal immunochemical test (FIT) have been implemented to reduce CRC mortality through early detection. Objectives To evaluate the association between an organized FIT-based screening program and CRC-specific mortality in a population-based setting. Design, Setting, and Participants This retrospective, population-based cohort study included all residents of the Basque Country, Spain (approximately 2.2 million inhabitants) between 2004 and 2024. The FIT-based CRC screening program targeting individuals aged 50 to 69 years was initiated in 2009. Individuals aged less than 50 years were included in the study as a nonscreening reference group. Data analysis was performed in April 2026. Exposure Biennial screening of asymptomatic individuals aged 50 to 69 years using single-sample FIT. Main Outcomes and Measures Age-standardized mortality rates (ASMRs) for CRC per 100 000 population (based on the European Standard Population 2013) and annual mortality trends from 2004 through 2024 were calculated. Segmented regression and counterfactual analyses estimated changes in CRC mortality after screening implementation. Screening participation, FIT positivity, colonoscopy adherence, CRC detection rates, and cancer stage distribution were also evaluated. Results Among 438 134 total deaths (50.9% in men) in a population of approximately 2.2. million, 16 298 (3.7%) were attributable to CRC. Age-standardized CRC mortality declined from 32.8 to 23.1 deaths per 100 000 population between 2004 and 2024 (reduction of 29.6%; P = .002). In individuals aged 50 to 69 years, CRC mortality declined by 50.1% (from 39.7 to 19.8 deaths per 100 000 population). Segmented regression identified a significant inflection point in the year 2012 (95% CI, 2011-2014; P lt; .001), 3 years after screening implementation. Counterfactual analyses estimated a 46.2% relative reduction in CRC mortality in the group aged 50 to 69 years compared with projected trends without screening. Among individuals aged 70 years or older, CRC mortality declined by 19.6% (from 165.4 to 132.9 deaths per 100 000 population), corresponding to a 45.4% relative reduction compared with projected rates. Overall, 3464 of 4892 screen-detected CRCs (70.8%) were diagnosed at stage I or II throughout the study period. Conclusions and Relevance In this retrospective, population-based, descriptive cohort study, organized FIT-based screening was associated with a sustained decline in CRC mortality, particularly among individuals aged 50 to 69 years. These findings support the long-term benefit of organized FIT-based screening programs as a public health strategy to reduce CRC-related mortality.