Screening outcomes at second FIT screening in individuals with a first time negative FIT-result or low-risk adenomas: Results from a nationwide FIT screening program

In Denmark, participants in faecal immunochemical test (FIT) screening with low-risk adenomas are recommended a return to biennial FIT-screening. However, they participate less than the FIT-negative group (FIT₁-negative) at subsequent screening. Further, it is not clear how much this group benefits from the subsequent screening. We aimed at comparing the CRC incidence before and at the next screening (FIT₂) in the low-risk group to that of those having a FIT-negative result at first time FIT-screening. In this register-based cohort study, we estimated the incidence of interval CRC (ICRC) and results of FIT₂, including the FIT₂-positivity rate and rate of screen detected CRC (SDCRC). Relative risk (RR) comparing the low-risk group to FIT₁-negatives was estimated. Adjustment for age and sex was performed with binary regression and presented with a 95% confidence interval (CI). Incidence of ICRC was 0.17% and 0.08% in the Low-risk group and FIT₁-negative group, respectively, RR 2.18 (95%CI 1.51; 3.16). After adjustment, RR was 1.76 (95%CI: 1.22; 2.55). The FIT₂-positivity rate was 14.4% and 4.4% for the Low-risk group and FIT₁-negative group, respectively. At FIT₂-screening, the detection of SDCRC was 0.36% and 0.16% in the low-risk and FIT₁-negative group, respectively, RR 2.27 (95%CI: 1.46; 3.54), adjusted 1.83 (95% CI: 1.17; 2.85). Despite a recent colonoscopy, participants having low-risk adenomas detected at first colonoscopy in FIT-screening remain at a higher short-term risk of ICRC and SDCRC compared to the FIT₁-negatives. Continuous participation in FIT-screening is important for the Low-risk group.