Plasma concentrations of polychlorinated biphenyls and the risk of breast cancer: a congener-specific analysis

Some reports indicate that exposure to specific polychlorinated biphenyl (PCB) congeners is related to breast cancer risk. The authors recruited participants in a case-control study from October 1994 to March 1997 to assess the relation between breast cancer risk and concentrations of 14 PCB congeners measured in plasma lipids by high-resolution gas chromatography. Participants were incident cases of breast cancer (n = 314) and controls (n = 523) from the Quebec City region (Canada). Compared with controls, cases had significantly higher concentrations of PCB 99 (p = 0.02), PCB 118 (p = 0.03), and PCB 156 (p = 0.006). Associations were found between breast cancer risk and either PCB 118 (odds ratio (OR) = 1.60, 95% confidence interval (CI): 1.01, 2.53; fourth vs. first quartile) or PCB 156 (OR = 1.80, 95% CI: 1.11, 2.94; fourth vs. first quartile) concentration. Breast cancer risk was also associated with a total concentration of the three mono-ortho-substituted congeners 105, 118, and 156 expressed as 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalents (OR = 2.02, 95% CI: 1.24, 3.28; fourth vs. first quartile). These results suggest that exposure to dioxin-like PCBs increases breast cancer risk. Alternatively, the results may be explained by differences between cases and controls regarding metabolic pathways involved in the biotransformation of both mono-ortho PCBs and estrogens.