Serum concentrations of organochlorine compounds and the subsequent development of breast cancer

A nested case-control study was conducted to examine the association betwee n serum concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE ), the primary metabolite of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and polychlorinated biphenyls (PCBs) and the development of breast c ancer up to 20 years later. Cases (n = 346) and controls (n = 346) were sel ected from cohorts of women who donated blood in 1974, 1989, or both, and w ere matched on age, race, menopausal status, and month and year of blood do nation. Analyses were stratified by cohort participation because median DDE and PCB concentrations among the controls were 59 and 147% higher in 1974 than 1989, respectively. Median concentrations of DDE were lower among case s than controls in both time periods [11.7% lower in 1974 (P = 0.06) and 8. 6% lower in 1989 (P = 0.41)]. Median concentrations of PCBs were similar am ong cases and controls [P = 0.21 for 1974 and P = 0.37 for 1989 (Wilcoxon s igned rank test)]. The risk of developing breast cancer among women with th e highest concentrations of DDE was roughly half that among women with the lowest concentrations, whether based on concentrations in 1974 [odds ratio (OR), 0.50; 95% confidence interval (CI), 0.27-0.89; P-trend = 0.02] or in 1989 (OR, 0.53; 95% CI, 0.24-1.17; P-trend = 0.08). The associations betwee n circulating concentrations of PCBs and breast cancer were less pronounced but still in the same direction (1974: OR, 0.68; 95% CI, 0.36-12.9; P-tren d = 0.2; and 1989: OR, 0.73; 95% CI, 0.37-1.46; P-trend = 0.6). Adjustment for family history of breast cancer, body mass index, age at menarche or fi rst birth, and months of lactation did not materially alter these associati ons. These associations remained consistent regardless of lactation history and length of the follow-up interval, with the strongest inverse associati on observed among women diagnosed 16-20 years after blood drawing. Results from this prospective, community-based nested case-control study are reassu ring. Even after 20 years of follow-up, exposure to relatively high concent rations of DDE or PCBs showed no evidence of contributing to an increased r isk of breast cancer.