Methods: Meta-analysis and review of 14 occupational cohort and four case-control studies of workers exposed to trichloroethylene (TCE) to investigate the relation between TCE exposure and the risk of non-Hodgkin’s lymphoma (NHL). Studies were selected and categorised based on a priori criteria, and results from random effects meta-analyses are presented.
Results: The summary relative risk estimates (SRRE) for the group of cohort studies that had more detailed information on TCE exposure was 1.29 (95% CI 1.00 to 1.66) for the total cohort and 1.59 (95% CI 1.21 to 2.08) for the seven studies that identified a specific TCE exposed sub-cohort. SRREs for three studies with cumulative exposure information were 1.8 (95% CI 0.62 to 5.26) for the lowest exposure category and 1.41 (95% CI 0.61 to 3.23) for the highest category. Comparison of SRREs by levels of TCE exposure did not indicate exposure-response trends. The remaining cohort studies that identified TCE exposure but lacked detailed exposure information had an SRRE of 0.843 (95% CI 0.72 to 0.98). Case-control studies had an SRRE of 1.39 (95% CI 0.62 to 3.10). Statistically significant findings for the Group 1 studies were driven by the results from the subgroup of multiple industry cohort studies (conducted in Europe) (SRRE = 1.86; 95% CI 1.27 to 2.71). The SRRE for single industry cohort studies was not significantly elevated (SRRE = 1.25; 95% CI 0.87 to 1.79).
Conclusions: Interpretation of overall findings is hampered by variability in results across the Group 1 studies, limited exposure assessments, lack of evidence of exposure response trends, lack of supportive information from toxicological and mechanistic data, and absence of consistent findings in epidemiologic studies of exposure and NHL. Although a modest positive association was found in the TCE sub-cohort analysis, a finding attributable to studies that included workers from multiple industries, there is insufficient evidence to suggest a causal link between TCE exposure and NHL.
- NHL, non-Hodgkin’s lymphoma
- SRRE, summary relative risk estimate
- PCE, perchloroethylene
- TCE, trichloroethylene
- non-Hodgkin’s lymphoma
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Published Online First 27 April 2006
Funding: This work was partially supported by unrestricted funds from the United States Air Force Institute for Operational Health, Brooks Air Force Base, San Antonio, TX (USAFIOH). The authors have consulted for a number of private and governmental clients on health issues related to occupational and environmental TCE exposure. JHM, DDA, MK, RK, PJM, and LY have received research funds from USAFIOH. MJK, MW, LY, and RK have received research funds from the TCE Issues Group, a group of companies involved in TCE remediation. JHM and LY have served as expert witnesses in matters involving TCE litigation. MK has received funds from the Halogenated Solvents Industry Association for a speaking engagement.
Competing interests: none declared