Spatio-temporal changes in clusters of gastric cancer incidence: The impact of nationwide cancer control programs in South Korea

BACKGROUND: Gastric cancer (GC) is a global health concern, with incidence and mortality varying significantly across populations. The spatial heterogeneity of GC may reflect differences in prevention strategies and their effectiveness, highlighting the need to identify high-risk areas and their possible contributing factors. OBJECTIVE: Leveraging the decline of GC incidence since 2012 affected by nationwide cancer prevention programs in South Korea, this study aimed to identify high- and low-risk clusters and explore the changes in spatial clusters of GC incidence between 2009-2013 and 2014-2018 before and after the decline, respectively. In addition, we identified geographic characteristics associated with cluster. METHOD: Using national cancer registry and geographic data across 243 districts, we performed spatial clustering analyses in each period. We identified the high- and low-risk areas as the overlapping clusters by two common clustering approaches of local Moran's I and Getis Ord Gi*. Then, we compared 23 geographic characteristics between high- and low-risk areas and two periods. RESULTS: The average GC incidence rate declined in both high- (96-79 per 100,000 people) and low-risk districts (73-61) between 2009-2013 and 2014-2018. While cluster locations remained stable, low-risk districts expanded notably (26-37) and high-risk districts slightly reduced (31-28). As opposed to little geographic characteristics that showed the significant difference between high- and low-risk areas in the early period, the later period gave large green space, frequent regular walking, and reduced self-related obesity in the low-risk area, in addition to sociodemographic advantages, compared to those in the high-risk area (p-value <0.002). CONCLUSION: Our findings suggest the potential effectiveness of lifestyle- and/or environment-focused prevention for GC incidence and the need of locally-tailored strategies to reduce cancer burden.