title: Occupational exposure to polychlorinated biphenyls and risk of breast cancer.
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.
  
  
  OBJECTIVE
  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.
authors.affiliation: National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluations and Field Studies, Cincinnati, Ohio 45226, USA. SSilver@cdc.gov
authors.forename: Sharon R
authors.initials: SR
authors.lastname: Silver
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Whelan
authors.forename: James A
authors.initials: JA
authors.lastname: Deddens
authors.forename: N Kyle
authors.initials: NK
authors.lastname: Steenland
authors.forename: Nancy B
authors.initials: NB
authors.lastname: Hopf
authors.forename: Martha A
authors.initials: MA
authors.lastname: Waters
authors.forename: Avima M
authors.initials: AM
authors.lastname: Ruder
authors.forename: Mary M
authors.initials: MM
authors.lastname: Prince
authors.forename: Lee C
authors.initials: LC
authors.lastname: Yong
authors.forename: Misty J
authors.initials: MJ
authors.lastname: Hein
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Ward
mesh_terms: D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D016273:Occupational Exposure / Q000009:adverse effects*; D011078:Polychlorinated Biphenyls / Q000009:adverse effects*; D012307:Risk Factors; D011795:Surveys and Questionnaires
chemical_list: D011078:Polychlorinated Biphenyls