Colorectal cancer incidence following a negative colonoscopy in fecal immunochemical test-based screening: a nationwide cohort study after 8 years of screening in Denmark

Background Screening participants with a positive fecal immunochemical test (FIT) result and a subsequent negative colonoscopy are quarantined from the Danish bowel cancer screening program for 8 years. This recommendation is based on evidence from settings other than FITbased screening, but referral of this evidence is not necessarily sufficient. We estimated the colorectal cancer (CRC) risk among these FIT-positive/colonoscopy-negative individuals and compared it with the risk in a historical unscreened population. Methods Using national health registers in Denmark, we compared 29 936 participants with a positive FIT but negative colonoscopy with 720 850 randomly selected unscreened controls born 9 years earlier (ratio 1:24). Controls were assigned a pseudo-colonoscopy date 9 years prior to the negative colonoscopy group. We examined cases per 10 000 person-years and estimated relative risks (RR) and 95%CIs for CRC. Results After 8 years' follow-up, CRC risk was lower among FIT-positive/colonoscopy-negative participants compared with controls (RR 0.72, 95%CI 0.61-0.84). By age group and sex, the lower risk was only evident for women and men in their 60 s (RR 0.67 [95%CI 0.47-0.96] and RR 0.65 [95%CI 0.48-0.88], respectively) and men in their 70 s (RR 0.60 [95%CI 0.44-0.84]). Conclusion The overall risk for CRC was lower for individuals with a positive FIT but negative colonoscopy compared with unscreened controls. However, the lower risk might not justify 8 years of quarantine, especially for women and younger age groups. Individualized screening is warranted and transfer of evidence from non-FIT screening should be done carefully.