Meta-analysis of lung cancer risk from exposure to diesel exhaust: study limitations.

Abstract

Vol. 122, No. 9 LetterOpen AccessMeta-Analysis of Lung Cancer Risk from Exposure to Diesel Exhaust: Study Limitations Kenny Crump Kenny Crump Search for more papers by this author Published:1 September 2014https://doi.org/10.1289/ehp.1408482Cited by:4AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Vermeulen et al. (2014) published a meta-analysis of the risk of lung cancer from exposure to diesel exhaust using data from three case–control studies—two of workers in the trucking industry (Garshick et al. 2012; Steenland et al. 1998) and one of workers in the mining industry (Silverman et al. 2012). Each of the studies quantified diesel exhaust exposure using cumulative exposure to elemental carbon. However, exposures in the trucking studies were lagged 5 years and those in the mining study were lagged 15 years. Vermeulen et al. (2014) applied these data in a linear regression that regressed the log odds ratio (logOR) versus cumulative lagged elemental carbon. They used the regression parameter from this analysis to predict lifetime excess risks for several lifetime occupational and environmental exposure scenarios, and also to predict the fraction of annual lung cancer deaths attributable to diesel exhaust. These excess risk calculations assumed a lag of 5 years.In their analysis, Vermeulen et al. (2014)inappropriately mixed data from exposures lagged 5 years and 15 years. The assumption of a 5-year lag used in the excess risk calculations is appropriate only if the exposures in all the underlying studies are also lagged 5 years. To obtain some idea of the quantitative effect of this error, I first reran the analysis of Vermeulen et al. (keeping the mixed lags), except that I did not model the dependence among the ORs from the same study. (I did not have access to data needed to model that dependence.) My analysis yielded a regression parameter [0.88; 95% confidence interval (CI): 0.65, 1.11] similar to that obtained by Vermeulen et al. (0.98; 95% CI: 0.55, 1.41). Next, I conducted the same analysis using this model, except I used all 5-year lags, obtaining (0.38; 95% CI: –0.03, 0.96). This analysis consequently yielded a considerably smaller slope, which was not statistically significantly different from 0. The predictions from my analysis were clearly consistent with the underlying ORs all plotted using a 5-year lag, whereas the predictions from the Vermeulen et al. model clearly were not [e.g., the OR at the highest 5-year lagged exposure was 1.25 (95% CI: 0.55, 2.84)]; the model of Vermeulen et al. (2014) predicted an OR of 5.5, and my model predicted an OR of 2.17). Similar results were obtained using a 0-year lag (5-year and 0-year were the only lag data to which we had access).There are other limitations of the analysis by Vermeulen et al. (2014): Garshick et al. (2012) employed a second measure of diesel exposure (exposure duration), which Vermeulen et al. did not account for in the analysis; and Vermeulen et al. used very crude exposure summaries (e.g., midpoints of exposure intervals).Estimates of excess risks should be based on the same lag that is common to the underlying studies. Consequently, it would be inappropriate to base public policy regarding exposures to diesel exhaust upon the meta-analysis of Vermeulen et al. (2014).Some of the results reported here are based on unpublished data underlying the case–control study by Silverman et al. (2012), and I express appreciation to the authors for their efforts in making these data available.The work reported in this letter was cofunded by a coalition of the following trade organizations: Truck and Engine Manufacturers Association, American Petroleum Institute, European Automobile Manufacturers Association, American Trucking Association, International Organization of Motor Vehicle Manufacturers, Alliance of Automobile Manufacturers, European Research Group on Environment and Health in the Transport Sector, Association of Equipment Manufacturers, Association of American Railroads, and European Association of Internal Combustion Engine Manufacturers.ReferencesGarshick E, Laden F, Hart JE, Davis ME, Eisen EA, Smith TJ. 2012. Lung cancer and elemental carbon exposure in trucking industry workers.Environ Health Perspect 120:1301-1306; doi:10.1289/ehp.120498922739103. Link, Google ScholarSilverman DT, Samanic CM, Lubin JH, Blair AE, Stewart PA, Vermeulen Ret al.. 2012. The Diesel Exhaust In Miners Study: a nested case–control study of lung cancer and diesel exhaust.J Natl Cancer Inst 104(11):855-86822393209. Crossref, Medline, Google ScholarSteenland K, Deddens J, Stayner L. 1998. Diesel exhaust and lung cancer in the trucking industry: exposure–response analyses and risk assessment.Am J Ind Med 34:220-2289698990. Crossref, Medline, Google ScholarVermeulen R, Silverman DT, Garshick E, Portengen L, Steenland K. 2014. Exposure–response estimates for diesel engine exhaust and lung cancer mortality based on data from three occupational cohorts.Environ Health Perspect 122:172-177; doi:10.1289/ehp.130688024273233. Link, Google ScholarFiguresReferencesRelatedDetailsCited by Morfeld P and Spallek M (2015) Dieselmotoremissionen und LungenkrebsrisikenDiesel motor emission and lung cancer risks, Zentralblatt für Arbeitsmedizin, Arbeitsschutz und Ergonomie, 10.1007/s40664-015-0021-4, 65:3, (133-148), Online publication date: 1-Jun-2015. Crump K, Van Landingham C, Moolgavkar S and McClellan R (2015) Reanalysis of the DEMS Nested Case-Control Study of Lung Cancer and Diesel Exhaust: Suitability for Quantitative Risk Assessment, Risk Analysis, 10.1111/risa.12371, 35:4, (676-700), Online publication date: 1-Apr-2015. Morfeld P and Spallek M (2015) Diesel engine exhaust and lung cancer risks – evaluation of the meta-analysis by Vermeulen et al. 2014, Journal of Occupational Medicine and Toxicology, 10.1186/s12995-015-0073-6, 10:1, Online publication date: 1-Dec-2015. Vermeulen R and Portengen L (2016) Is diesel equipment in the workplace safe or not?: Table 1, Occupational and Environmental Medicine, 10.1136/oemed-2016-103977, (oemed-2016-103977) Vol. 122, No. 9 September 2014Metrics About Article Metrics Publication History Originally published1 September 2014Published in print1 September 2014 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. 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