Occupational heat exposure and prostate cancer risk: a pooled analysis of case-control studies

Background and aim: Heat exposures occur frequently in many indoor and outdoor occupations. In our previous work, we observed some evidence for a positive association of occupational heat exposure and breast cancer risk. Here we seek to examine potential associations with prostate cancer risk in a large multi-country study. Methods: We performed a pooled analysis of data from 3,175 histologically confirmed prostate cancer cases and 3,529 frequency-matched controls from studies in three different countries, Spain, France, and Canada. The Finnish job exposure matrix, FINJEM, was used to apply estimates of occupational heat exposure to the lifetime occupational history of participants. Three main exposure indices were used: ever vs. never exposed, lifetime cumulative exposure (heat stress years) and duration of exposure (years) with a lag period of 5 years. We estimated odds ratios (ORs) and 95% confidence intervals (CIs), using conditional logistic regression models stratified by 5-year age groups and study and adjusted for potential confounders. Results: A total of 32% of cases and 33% of controls were classified as being ever occupationally exposed to heat. Highest heat exposed occupations included ore and metal furnace operators, firefighters, and bakers. We found no evidence for an association of ever occupational heat exposure and prostate cancer risk (OR 0.92; 95% CI 0.83, 1.03). There were also no associations observed in the highest categories of lifetime cumulative exposure or duration, and there was no evidence for a trend. Results did not change when stratifying by Gleason scores. When analysing the Spanish case-control study separately using a Spanish job exposure matrix developed for local working conditions, some odds ratios were elevated, though results were imprecise. Conclusions: Findings from this pooled study have provided no strong evidence for an association between occupational heat exposure and prostate cancer risk. Keywords: prostate cancer, occupational exposures, heat, pooled analysis