title: Joint effects of nine polychlorinated biphenyl (PCB) congeners on breast cancer risk.
abstract: BACKGROUND
  Polychlorinated biphenyls (PCB) have been a major environmental health concern because of their wide distribution and persistence in the environment. Estimating joint effects of all congeners in a single analysis is complicated by correlation among exposure levels, and the resulting collinearity makes the results difficult to interpret.
  
  
  METHODS
  Patients with breast-related surgery at Yale-New Haven Hospital were interviewed using a standardized questionnaire, and breast adipose tissue samples were analysed for nine PCB congeners (74, 118, 138, 153, 156, 170, 180, 183, 187). The study recruited 490 women (304 cases and 186 controls) between 1994 and 1997. Logistic ridge regression was used to analyse the instability caused by collinearity.
  
  
  RESULTS
  Although total PCB did not appear to be associated with breast cancer risk, significant differences in effect were observed among the nine congeners. Logistic ridge regression demonstrated a protective effect on breast cancer risk for a potentially anti-oestrogenic and dioxin-like congener, 156, while two phenobarbital, CYP1A and CYP2B inducers had an adverse effect, 180 and 183. This analysis also suggested that a protective effect for another phenobarbital congener, 153, was largely explained by instability caused by collinearity.
  
  
  CONCLUSIONS
  These results indicate that studies of PCB congeners and health require an in-depth statistical analysis in order to better understand the complex issues related to their collinearity.
authors: Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT 06520-8034, USA.
authors: T R
authors: TR
authors: Holford
authors: T
authors: T
authors: Zheng
authors: S T
authors: ST
authors: Mayne
authors: S H
authors: SH
authors: Zahm
authors: J D
authors: JD
authors: Tessari
authors: P
authors: P
authors: Boyle
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry; D000328:Adult; D000368:Aged; D001940:Breast / Q000737:chemistry; D001943:Breast Neoplasms / Q000139:chemically induced / Q000453:epidemiology*; D004785:Environmental Pollutants / Q000009:adverse effects / Q000032:analysis; D005260:Female; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D011078:Polychlorinated Biphenyls / Q000009:adverse effects / Q000032:analysis; D012306:Risk
chemical_list: D004785:Environmental Pollutants; D011078:Polychlorinated Biphenyls