Long-Term Effectiveness Associated With Fecal Immunochemical Testing for Early-Age Screening

Importance The rising incidence of young-onset colorectal cancer (CRC) has prompted health policymakers to consider lowering the recommended starting age for screening. However, population-based evidence supporting the long-term effectiveness of early-age screening remains limited. Objective To evaluate whether initiating fecal immunochemical test (FIT) screening at ages 40 to 49 years, rather than at the currently recommended age of 50 years, reduces CRC incidence and mortality. Design, Setting, and Participants This study analyzed a community-based screening cohort of Taiwanese residents aged 40 to 49 years, categorized into 4 subcohorts based on participation in early screening (age 40 to 49 years) and continuation of nationwide regular screening (50 years and older). The cohort was followed up until 2019 to compare CRC incidence and mortality across subcohorts. To mitigate self-selection bias, a delayed screening design and efficient propensity score matching was used, restricting analyses to participants attending regular screening. To validate the findings, an extended nonadherence adjustment was applied to all 4 subcohorts. Data were collected from January 2001 to December 2019, and data were analyzed from January 2021 to December 2024. Exposures Biennial FIT screening was initiated for the early screening group at ages 40 to 49 years and for the regular screening group at age 50 years, with follow-up continuing under Taiwan’s national screening program. Main Outcomes and Measures Primary outcomes were CRC incidence and mortality rates, reported as cases per 100 000 person-years, with adjusted relative risks (aRRs) comparing early vs regular screening groups. Results Of 263 125 included participants, 146 796 (55.8%) were female. A total of 39 315 participated in early and regular screening, and 223 810 participated in regular screening only. The early screening group exhibited lower CRC incidence (26.1 [95% CI, 22.3-29.9] vs 42.6 [95% CI, 40.5-44.7] per 100 000 person-years) and mortality (3.2 [95% CI, 1.9-4.6] vs 7.4 [95% CI, 6.5-8.2] per 100 000 person-years). In propensity score–matched analyses, early screening significantly reduced CRC incidence (aRR, 0.79; 95% CI, 0.67-0.94) and mortality (aRR, 0.61; 95% CI, 0.38-0.98). Findings were consistent in the extended nonadherence adjustment model, showing a 25% reduction in incidence (aRR, 0.75; 95% CI, 0.72-0.77) and a 34% reduction in mortality (aRR, 0.66; 95% CI, 0.62-0.71). Conclusions and Relevance This study found that initiating FIT screening at age 40 to 49 years was associated with further reduction in CRC mortality and incidence compared with starting screening at age 50 years. These results provide strong empirical support for lowering the CRC screening age, with substantial public health implications.