A reanalysis of Sweden’s population-based colorectal cancer screening program suggests that the mortality benefit of fecal occult blood testing (FOBT) may have been underestimated. In a prospective cohort of 376,511 adults ages 60–69, researchers adjusted for two sources of contamination: people in the screening group who developed CRC more than two years after their last invitation, and controls who were later invited to screening. After these adjustments, invitation to screening was associated with a 26% reduction in CRC mortality.
When the analysis additionally accounted for nonadherence, participation in screening was associated with a 43% reduction in CRC mortality (RR, 0.57; 95% CI, 0.40–0.80). The authors emphasize that the findings illustrate how contamination and nonadherence can dilute estimates of screening effectiveness and support efforts to increase screening uptake.