| Occupational Exposure to Polychlorinated Biphenyls and Risk of Breast Cancer Sharon R. Silver,1 Elizabeth A. Whelan,1 James A. Deddens,1 N. Kyle Steenland,2 Nancy B. Hopf,3 Martha A. Waters,1 Avima M. Ruder,1 Mary M. Prince,4 Lee C. Yong,1 Misty J. Hein,1 and Elizabeth M. Ward5 1National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluations and Field Studies, Cincinnati, Ohio, USA; 2Department of Epidemiology, Emory University School of Public Health, Atlanta, Georgia, USA; 3Department of Environmental Health, University of Cincinnati, Cincinnati, Ohio, USA; 4Sanofi-aventis, Bridgewater, New Jersey, USA; 5American Cancer Society, Atlanta, Georgia, USA Abstract
Background: Despite the endocrine system activity exhibited by polychlorinated biphenyls (PCBs) , recent studies have shown little association between PCB exposure and breast cancer mortality. Objectives: To further evaluate the relation between PCB exposure and breast cancer risk, we studied incidence, a more sensitive end point than mortality, in an occupational cohort. Methods: We followed 5,752 women employed for at least 1 year in one of three capacitor manufacturing facilities, identifying cases from questionnaires, cancer registries, and death certificates through 1998. We collected lifestyle and reproductive information via questionnaire from participants or next of kin and used semiquantitative job-exposure matrices for inhalation and dermal exposures combined. We generated standardized incidence ratios (SIRs) and standardized rate ratios and used Cox proportional hazards regression models to evaluate potential confounders and effect modifiers. Results: Overall, the breast cancer SIR was 0.81 (95% confidence interval, 0.72–0.92 ; n = 257) , and regression modeling showed little effect of employment duration or cumulative exposure. However, for the 362 women of questionnaire-identified races other than white, we observed positive, statistically significant associations with employment duration and cumulative exposure ; only smoking, birth cohort, and self- or proxy questionnaire completion had statistically significant explanatory power when added to models with exposure metrics. Conclusions: We found no overall elevation in breast cancer risk after occupational exposure to PCBs. However, the exposure-related risk elevations seen among nonwhite workers, although of limited interpretability given the small number of cases, warrant further investigation, because the usual reproductive risk factors accounted for little of the increased risk. Key words: breast cancer, incidence, occupational epidemiology, polychlorinated biphenyls. Environ Health Perspect 117:276–282 (2009) . doi:10.1289/ehp.11774 available via http://dx.doi.org/ [Online 26 September 2008]
Address correspondence to S.R. Silver, Industrywide Studies Branch, DSHEFS, NIOSH, 4676 Columbia Parkway, R-15, Cincinnati, OH 45226 USA. Telephone: (513) 841-4313. Fax: (513) 841-4486. E-mail: SSilver@cdc.gov We thank M. Schubauer-Berigan, P. Laber, C. Gersic, F. Armstrong, C. Lehman, Z. Zivkovich, T. Schnorr, and M. Torok for their assistance with this study. The assistance of the following cancer registries was also invaluable: the Massachusetts Department of Public Health, Massachusetts Cancer Registry ; the New York State Department of Health, New York State Cancer Registry ; Indiana State Department of Health, Indiana State Cancer Registry ; California Cancer Registry ; and the Florida Cancer Data System. This study was supported, in part, by the Department of Defense Women’s Health Research Program (MIPR 94MM4580) . The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. The authors declare they have no competing financial interests. Received 9 June 2008 ; accepted 25 September 2008.
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