Impact of South Koreas national gastrointestinal cancer screening programme on incidence and mortality: a population-based difference-in-differences study

Objectives The objectives of this study were threefold. First, to examine the long-term association between implementation of South Korea's National Cancer Screening Programme and trends in incidence and mortality for major gastrointestinal cancers at the population level.

Second, to assess whether programme-associated effects differed across implementation phases and population subgroups defined by age, sex and region. Third, to evaluate the specificity of observed trends by comparing screened cancers with pancreatic cancer, which is not included in the national screening programme, using a quasi-experimental difference-in-differences approach.

Design Population-based quasi-experimental study using a difference-in-differences approach. Setting Nationwide analysis using publicly available national cancer registry, screening and mortality data obtained from Statistics Korea (Korean Statistical Information Service) and related national databases.

We applied a quasi-experimental difference-in-differences design comparing pre-intervention (1999 - 2002), early implementation (2003 - 2011) and long-term effect (2012 - 2021) periods, reflecting the expected latency between screening implementation and population-level outcome changes. Participants Individuals eligible for NCSP screening based on age and programme criteria between 1999 and 2021, compared with contemporaneous populations not eligible for screening.