We conducted a meta-analysis of occupational studies of trichloroethylene-exposed workers to evaluate patterns of associations by study design, exposure assessment methods, and occupational groups.
Estimates of summary relative risk (RR) were calculated using inverse-variance weighting methods. Cohort studies were classified as group I or group II, depending on quality of the study design and exposure assessment procedures. We conducted sensitivity analyses to examine sources of heterogeneity.
Across all studies meeting our inclusion criteria (n = 23), the summary RR was 1.42 (95% confidence interval = 1.17–1.77), with heterogeneity present (test for heterogeneity: P = 0.001). After removal of 3 outlier studies, the summary RR for the remaining studies was 1.24 (1.06–1.45 (test for heterogeneity: P = 0.616)). The summary RR for studies of workers who were identified as more likely exposed to trichloroethylene (group I studies) was 1.34 (1.06–1.68). With outlier studies removed, the group II summary RR estimates for the cohort studies was 0.88 (0.58–1.33) and for the case-control studies was 1.33 (1.02–1.73). The summary RR for studies that used biomarkers to classify exposure (n = 3) was 1.02 (0.59–1.77) and for studies of aerospace/aircraft workers (n = 7) was 1.14 (0.84–1.57).
Positive associations were observed across various study groups. However, considerations of unmeasured potential confounding, lack of quantitative exposure assessment and lack of exposure-response patterns limit epidemiologic insight into the role of trichloroethylene exposure and its potential causal association with kidney cancer.
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From the aHealth Science Practice, Exponent, Inc, Menlo Park, CA; bHealth Science Practice, Exponent, Inc, Chicago, IL; cHealth Science Practice, Exponent, Inc, Washington, DC; dDepartment of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA; and eDivision of Environmental Health Sciences, School of Public Health, University of Minnesota, Minneapolis, MN.
Submitted 13 January 2009; accepted 24 June 2009.
Supported by the TCE Issues Group and the Halogenated Solvents Industry Association.
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Correspondence: Michael A. Kelsh, Exponent, Inc, 149 Commonwealth Dr, Menlo Park, CA 94025. E-mail: firstname.lastname@example.org.