Plasma organochlorine levels and the risk of breast cancer: an extended follow-up in the nurses' health study

The environmental organochlorines 2,2-bis(p-chlorophenyl)1,1,1,trichloroeth ane (DDT) and polychlorinated biphenyls (PCBs) have been implicated as pote ntial causes of female breast cancer. We continued follow-up of our 1997 ca se control study nested in the Nurses' Health Study cohort, adding 143 post menopausal cases and controls to the original 238 pairs, and examining spec ific PCB congeners for the first time. We measured plasma levels of 2,2-bis (p-chlorophenyl)ethylene (DDE), the major metabolite of DDT, and PCBs prosp ectively, comparing women who were diagnosed with breast cancer between I m onth and 4 years after blood collection with control women in whom breast c ancer did not develop, Median concentrations of lipid-adjusted DDE, total P CBs, and PCB numbers 118, 138, 153 and 180, assessed individually, were sim ilar among the cases and controls. The multivariate relative risk of breast cancer for women in the highest quintile of exposure as compared with wome n in the lowest quintile was 0.82 for DDE (95% confidence interval [Cl]: 0. 49-1.37) and 0.84 for total PCBs (95% Cl: 0.47-1.52), 0.69 for PCB 118 (95% Cl: 0.39-1.22), 0.87 for PCB 138 (95% Cl: 0.50-1.50), 0.83 for PCB 153 (95 % Cl: 0.47-1.48), and 0.98 for PCB 180 (95% Cl: 0.55-1.75), Sub-group analy ses were also performed. Overall, our results do not support the hypothesis that exposure to DDT and PCBs increases the risk of breast cancer. (C) 200 1 Wiley-Liss, Inc.