Incremental Value of Adherence to Repeat Stool Test in Reducing Long-term Incidence of Colorectal Cancer

INTRODUCTION: Annual stool testing with fecal occult blood testing (FOBT) or fecal immunochemical test (FIT) is commonly used for colorectal cancer screening but the incremental benefit of adherence to multiple rounds of stools tests for long-term reduction in CRC incidence has not been studied. Our aims were to study the incremental effect of repeat annual FOBT on 20-year CRC incidence in an average-risk screen-eligible population. METHODS: We used data from the Minnesota Colon Cancer Control Clinical trial, which enrolled 45,661 individuals to undergo annual biennial or no screening. We studied the difference in 20-year CRC incidence between those who do and do not complete each round of screening, from round 1 to round 4, in the annual arm. RESULTS: Overall, 13,130 participants from the annual arm completed the first round of screening, and 12,638 were eligible for round 2, 10,863 were eligible for round 3 and 9206 were eligible for round 4. The adjusted risk of CRC at 20 years for those who completed round 2 was 1.60 (95% CI: 0.34-2.87) percentage points lower than that of those who did not. The adjusted 20-year incidence of CRC in those who completed rounds 3 and 4 was 0.51 (95% CI: -0.73, 1.75) and 0.08 (95% CI: -1.19, 1.35) percentage point lower than those who did not complete rounds 3 and 4, respectively, and was not statistically significant. CONCLUSIONS: Our study underscores the importance of adherence to more than 1 round of screening and provides information for providers and patients about the benefits they may accrue from at least 2 rounds of adherence. We also found that the overall value of repeat screening after 2 negative rounds is important but provides marginal gain. The implications are that perfect adherence over multiple rounds may not be necessary to accrue the benefits of a reduction in CRC incidence and mortality.