FIT or Colonoscopy? Adherence May Matter More Than the Test
Review by Dr. Burcu Gurbuz (Turkey)
Study Summary
Colonoscopy and fecal immunochemical testing (FIT) are both effective colorectal cancer (CRC) screening strategies, but comparing them is complicated by a fundamental real-world problem: people do not adhere equally to each approach. Previous intention-to-screen results from the COLONPREV randomized trial showed similar long-term CRC outcomes despite substantially greater participation with FIT. Whether outcomes remain comparable among individuals who actually initiate and continue their assigned screening strategy has been less clear.
Castells and colleagues performed a post hoc sustained-strategy analysis of 17,270 COLONPREV participants aged 50–69 years from eight regions of Spain who initiated screening. The analysis compared one colonoscopy with a strategy of biennial FIT at years 0, 2, 4, 6, and 8, with colonoscopic assessment following a positive FIT. Inverse probability weighting was used to address measured differences between groups and informative deviations from the screening protocol.
At 10 years, weighted CRC incidence was remarkably similar with sustained FIT and colonoscopy (0.80% vs. 0.86%). All-cause mortality was also almost identical (4.02% vs. 4.09%). CRC mortality was numerically lower following colonoscopy (0.042% vs. 0.072%), but the number of events was small and the estimate was imprecise. Overall, among people who initiated and adhered to screening, sustained biennial FIT and one-time colonoscopy produced broadly similar 10-year outcomes, shifting attention from the theoretical superiority of an individual test toward the practical importance of maintaining participation in a screening program.
Commentary
The most important message from this study may not be that FIT and colonoscopy are equivalent, but that adherence is part of the treatment. Colonoscopy offers high diagnostic sensitivity and the opportunity for immediate polypectomy, but its benefits cannot be realized when individuals decline the procedure. FIT is less invasive and easier to deploy at scale, but its effectiveness depends on repeated testing and timely colonoscopy following a positive result. COLONPREV therefore addresses a question of particular relevance to population screening: what happens when screening is considered as a sustained pathway rather than a single test?
Several cautions are essential. This was a post hoc rather than prespecified comparison, and adherence itself was not randomized. Statistical weighting can reduce measured selection bias but cannot eliminate bias from unmeasured differences between participants. Moreover, 68.8% of FIT initiators experienced per-protocol censoring before the end of follow-up, predominantly because a subsequent FIT round was missed. CRC deaths were uncommon, leaving the mortality comparison particularly imprecise.
Despite these limitations, the study has considerable global relevance. Many health systems cannot offer primary screening colonoscopy to an entire eligible population because of limited endoscopy capacity, cost, or workforce constraints. A well-organized FIT program with reliable recall systems and prompt colonoscopy after a positive result may therefore provide an effective and scalable alternative. The next challenge is less about declaring a universal winner between FIT and colonoscopy and more about designing programs that people will enter—and continue. Screening policy should consider patient preference, local resources, and sustained adherence alongside test performance.
Citation
Castells A, Quintero E, Chen H, et al. Colonoscopy versus biennial FIT screening: a post hoc sustained-strategy analysis of the COLONPREV Trial. Gut. Published online June 10, 2026. doi:10.1136/gutjnl-2026-338896.
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