101 Occupational exposure to tetrachloroethylene and the risk of bladder cancer: A meta-analysis

Objectives The risk of bladder cancer in persons occupationally exposed to tetrachloroethylene was summarised using a meta-analysis. Methods Studies were identified from a Pubmed literature search including the terms “drycleaner, dry-cleaning, occupation, tetrachloroethylene, bladder cancer, bladder carcinoma, urothelial carcinoma” in various combinations. We included studies that reported a risk estimate specifically for tetrachloroethylene or employment as a “dry cleaner” based on historical information indicating that a large percentage of drycleaners were exposed to tetrachloroethylene but not to other occupational bladder carcinogens. We excluded studies that reported results for “dry-cleaners and laundry workers” (the latter group has not been exposed to tetrachloroethylene), PMR analyses (risk estimates are potentially biassed), and overlapping publications. Publication bias was assessed using funnel plots. All statistical analyses were performed using STATA. Results Twelve studies were included in the meta-analysis (8 case-control studies, 4 cohort studies) resulting in a meta-RR of 1.24 (95% CI, 1.12–1.37). The meta-RR was 1.20 (95% CI, 1.07–1.34) for case-control studies (all adjusted for smoking) and 1.44 (95% CI, 1.13–1.84) among the cohort studies (none adjusted for smoking). When we restricted the analysis to the studies reporting a risk estimate specifically for exposure to tetrachloroethylene the meta-RR was 1.18 (95% CI: 1.05–1.33; 3 studies) and for dry cleaners it was 1.46 (95% CI: 1.17–1.83; 9 studies). A jack knife analysis omitting individual studies demonstrated that there was no overreliance of the overall meta-RR on a single study. There was no evidence of publication bias. One of the included studies assessed exposure-response data and reported an increase in odds ratios with increasing cumulative exposure among men. Conclusions Occupational exposure to tetrachloroethylene is associated with a moderate, significantly increased risk of bladder cancer. Excesses occurred in cohort and case-control studies. The excesses in case-control studies could not be explained by tobacco use.