Prospective cohort study of fecal occult blood screening outcomes adjusted for contamination bias and nonadherence

Population-based colorectal cancer (CRC) screening with fecal occult blood tests (FOBT) is widely implemented. Estimating associations of invitation to and participation in the screening program with CRC mortality is challenging due to lack of valid control groups and uncertainties about optimal follow-up duration. A prospective cohort study in Sweden investigated the associations of invitation to and participating in FOBT screening with CRC mortality reduction when adjusting for death from CRC diagnosed more than 2 years after cessation of screening and for nonadherence. In this study of 376 511 individuals with up to 14 years of follow-up, invitation to screening was associated with a statistically significant 26% reduction in CRC mortality (rate ratio 0.74; 95% CI 0.58-0.94). Adjusting for nonadherence among invitees, participation in screening was associated with a statistically significant 43% reduction in CRC mortality (RR 0.57; 95% CI 0.40-0.80). The authors conclude that these findings suggest that invitation to participate in population-based FOBT screening may prevent more than 25% of CRC deaths and participating in screening may prevent more than 40% of CRC deaths.