Occupational heat exposure and stomach cancer risk in a pooled analysis of two Spanish case-control studies in the stomach cancer pooling project – StoP consortium

Background: Occupational heat stress occurs frequently and is increasing with climate change. Studies of occupational heat exposure and stomach cancer risk are limited. We used data from the international Stomach cancer Pooling (StoP) Project to investigate the relationship between occupational heat exposure and stomach cancer risk in a pooled analysis of two Spanish case-control studies, including 566 stomach cancer cases and 2984 controls. Methods: The Spanish job-exposure matrix, MatEmEsp, was used to assign heat exposure estimates to participant occupations. We evaluated three exposure indices: ever vs. never exposed, cumulative exposure and duration (years). We calculated odds ratios (ORs) and corresponding 95 % confidence intervals (CIs) using unconditional logistic regression models including terms for potential confounders. Results: Overall, 60.6 % of cases and 42.7 % of controls were ever occupationally exposed to heat. Occupational heat exposure was associated with a moderately elevated risk of stomach cancer (OR 1.31; 95 % CI 1.05, 1.63) when comparing ever vs. never exposed individuals in both studies combined. Elevated ORs were also observed across categories of cumulative exposure and duration (p-trend = 0.01 and 0.03, respectively). Findings were robust to additional covariate adjustment and in analysis of never smokers. There was no clear evidence for interaction according to exposure status to other suspected occupational stomach carcinogens. Conclusion: Findings from this study provide some evidence for a positive association between occupational heat exposure and stomach cancer risk. Further research is needed to advance occupational heat assessment tools for epidemiological research as well as studies in more geographically diverse populations.