Polychlorinated biphenyls and their association with survival following breast cancer

Background Polychlorinated biphenyls (PCBs) are hypothesised to influence breast carcinogenesis due to their persistence and potential to induce oestrogenic and anti-oestrogenic effects. Whether PCBs influence survival following breast cancer is unknown. Methods A population-based cohort of women diagnosed with first primary invasive or in situ breast cancer in 1996-1997 and with blood-measured PCBs (n=627) collected shortly after diagnosis was followed for vital status through 2011. After 5 and 15 years, we identified 54 and 187 deaths, respectively, of which 36 and 74 were breast cancer related. Using Cox regression, we estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for mortality for baseline PCB concentrations, individually and as oestrogenic (ΣGroup 1B: PCB101, PCB174, PCB177, PCB187, and PCB199), anti-oestrogenic (ΣGroup 2A: PCB66, PCB74, PCB105, and PCB118; ΣGroup 2B: PCB138 and PCB170), and cytochrome P450 enzyme-inducing (ΣGroup 3: PCB99, PCB153, PCB180, PCB183, and PCB203) groups. Results The highest PCB174 tertile was associated with an increase in all-cause (HR=2.22, 95% CI: 1.14-4.30) and breast cancer-specific (HR=3.15, 95% CI: 1.23-8.09) mortalities within 5 years of diagnosis and remained associated with breast cancer-specific mortality (HR=1.88, 95% CI: 1.05-3.36) at 15 years. At 5 years, the highest tertile of PCB177 was positively associated with all-cause mortality (HR=2.12, 95% CI: 1.05-4.30). At 15 years, the highest tertiles of ΣGroup 2A congeners and PCB118 were inversely associated with all-cause mortality (HR=0.60, 95% CI: 0.39-0.83; HR=0.63, 95% CI: 0.43-0.92, respectively). Conclusions In this first US study of PCBs and breast cancer survival, PCBs were associated with mortality in biologically plausible directions. The investigation of other, structurally similar, chemicals may be warranted.