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

## TL;DR

Gastric cancer survivors have a slightly higher long-term risk of pneumonia, especially in certain groups like men and those with lower socioeconomic status.

## Contribution

This study is the first to use a nationwide Korean cohort to show a long-term pneumonia risk in gastric cancer survivors beyond treatment-related complications.

## Key findings

- GC survivors had a 6% higher risk of pneumonia compared to controls.
- Higher pneumonia risk was observed in men, socioeconomically disadvantaged individuals, and urban residents.
- Patients without comorbidities also showed increased pneumonia risk.

## Abstract

Gastric cancer (GC) patients are increasingly surviving longer due to improved screening and treatment. However, survivors may remain vulnerable to respiratory complications such as pneumonia. Using a large, nationwide cohort from Korea, we investigated the long-term risk of pneumonia following GC diagnosis. We found that GC patients had a modest but significant elevation in pneumonia risk, particularly among men, socioeconomically disadvantaged individuals, urban residents, and patients without comorbidities. These findings may emphasize the necessity of ongoing pneumonia monitoring and preventive care in GC survivorship.

Background/Objectives: 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. Methods: 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. Results: 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. Conclusions: 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.