Long-Term Risk of Pneumonia Among Gastric Cancer Survivors: A Nationwide Population-Based Cohort Study

Gastric cancer (GC) remains a major global health burden, but its long-term association with pneumonia risk has not been comprehensively investigated. This study aimed to evaluate the long-term risk of pneumonia among GC survivors using a nationwide Korean cohort, focusing on chronic post-cancer susceptibility rather than perioperative or treatment-related complications.

We conducted a nationwide, population-based cohort study using the Korean National Health Insurance Service database, including 9212 GC patients and 36,848 age-, sex-, income-, and region-matched controls (1:4 ratio). Participants were followed for up to 17 years. Propensity score overlap weighting was applied to minimize confounding, achieving exact covariate balance and optimal precision, with standardized differences used to confirm balance. Adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) for pneumonia were estimated via Cox proportional hazards models.

During follow-up from 2002-2003 through 2019 (maximum 17 years), GC showed a significant relationship with increased risk of pneumonia (aHR 1.06; 95% CI: 1.01-1.11; p = 0.014). Subgroup analyses revealed higher risks among men, socioeconomically disadvantaged individuals, urban residents, and unexpectedly, patients without comorbidities.

This large nationwide cohort study demonstrated that GC may be linked to a slightly elevated long-term risk of pneumonia, varying across demographic and clinical subgroups. These findings underscore the need for continued respiratory health monitoring in GC survivors while acknowledging that the observed association may be influenced by underlying comorbidities and survivorship factors.