The impact of an organized screening program on gastric cancer incidence: a quasi-experimental study.

[BACKGROUND] Evidence of gastric cancer (GC) screening's impact on GC incidence remains limited. In 2002, South Korea started a nationwide GC screening program. This study uses a quasi-experimental design to evaluate the effect of the program on GC incidence in Seoul.

[METHODS] Using a flexible synthetic control method (SCM), we estimated the impact of GC screening on age-standardized GC incidence in Seoul. Annual age-specific GC incidence data were obtained from the Seoul Cancer Registry and Cancer Incidence in Five Continents Plus database. Post-intervention trends in GC incidence between Seoul and the synthetic control were compared to estimate average rate ratios (RRs) with 95% confidence intervals (CIs). Several sensitivity and alternative analyses were performed, including a modified age-period-cohort (APC) analysis.

[RESULTS] The screening program was associated with a higher GC incidence in Seoul compared to the synthetic control, with an average post-intervention RR of 1.11 (95% CI: 0.99-1.24). After 2002, the start of the screening program, there was a noticeable increase in the post-intervention differences between Seoul and the synthetic control, which peaked in 2011 (RR 1.26), and then began to fall. The results were robust across sensitivity analyses and alternative analyses. The modified APC analysis indicated that after initially expanding and then diminishing, the effect eventually reversed, resulting in a reduction in incidence.

[CONCLUSIONS] These findings suggest that healthcare sectors should anticipate an immediate increase in care demands following GC screening implementation. While a subsequent reduction in GC incidence is expected, the potential preventive impact remains inconclusive.