Environmental Tobacco Smoke and Gastric Cancer: Evidence from the Stomach Cancer Pooling (StoP) Project and a Comprehensive Meta-analysis

BACKGROUND: Few studies have investigated environmental tobacco smoke (ETS), commonly known as secondhand smoke, and gastric cancer (GC) risk, and the findings have been inconsistent. We conducted a pooled analysis from StoP Project and a comprehensive meta-analysis to evaluate the potential impact of ETS exposure on GC risk. METHODS: Five case-control studies with ETS information from the StoP project were included (1,560 GC cases and 2,497 controls). Study-specific odds ratios (ORs) and the corresponding 95% confidence intervals (CI) were estimated using unconditional logistic regression models, adjusting for potential confounders. Pooled effect estimates were computed using random-effects models, with heterogeneity assessed using I2 (%) statistics. A comprehensive meta-analysis was conducted including the StoP project and published studies (n=14), with publication bias assed via funnel plot and Egger's test. RESULTS: Study-specific estimates were heterogeneous, with stronger associations observed among never-smokers. A strong positive association was observed in the Iran study (aOR = 2.38; 95%CI: 1.11, 5.09) among never-smokers. ETS exposure was not associated with GC risk in the pooled StoP analysis. In the comprehensive meta-analysis, the H. pylori-adjusted subgroup showed a positive association (aOR = 1.41; 95% CI: 1.21-1.64). The overall aOR was 1.25 (95% CI: 0.98-1.59, I2 = 69.9%). CONCLUSIONS: The results support the hypothesis that ETS could be a risk factor for GC, underscoring the importance of targeted preventive measures and public health policies to reduce ETS exposure. IMPACT: This study provides the most comprehensive evaluation to date of ETS exposure and highlights ETS as a preventable GC risk factor.