Background: Polychlorinated biphenyls (PCBs) are a group of 209 synthetic organic chemicals, several of which are known carcinogens or endocrine disruptors. PCBs are hypothesized to influence the risk of developing breast cancer; however, whether PCBs influence the risk of mortality following breast cancer is poorly understood. We examined plasma levels of 17 PCB congeners in association with mortality among women who participated in the population-based Carolina Breast Cancer Study (CBCS). Methods: Participants included 456 white and 292 black women who were diagnosed with primary invasive breast cancer from 1993-1996, and who had PCB and lipid measurements from blood samples obtained on average 4.1 months after diagnosis. Using the National Death Index, we identified 392 deaths including 210 from breast cancer, over a median follow-up of 20.6 years. We used Cox regression to estimate covariate-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause and breast cancer-specific 5-year mortality, and 20-year mortality conditional on 5-year survival in relation to tertiles and continuous ln-transformed lipid-adjusted PCB levels. We also examined effect measure modification by race. Results: The highest (vs. lowest) tertile of PCB118 was associated with a 5-year breast cancer-specific mortality HR of 1.86 (95% CI=1.07-3.23). One-ln unit increases in PCB74, PCB99, PCB118, and total PCBs were associated with 5-year breast cancer-specific mortality HRs ranging from 1.33 (95% CI=1.02-1.74) for PCB74 to 1.40 (95% CI=1.02-1.92) for PCB118. By race, a one-ln unit increase in PCB74 was associated with a HR of 1.47 (95% CI=1.01-2.14) among black women and with a HR of 1.19 (95% CI=0.79-1.77) among white women (P-Interaction=0.05). Continuous PCB levels were associated with 20-year conditional all-cause mortality HRs ranging from 1.20 (95% CI=1.03-1.41) for a one-ln unit increase in PCB182+PCB187 to 1.37 (95% CI=1.12-1.68) for a one-ln unit increase in PCB118. PCBs were not associated with 5-year all-cause mortality or with 20-year conditional breast cancer-specific mortality. Conclusion: PCBs may increase the risk of short-term breast cancer-specific mortality as well as long-term all-cause mortality among women with breast cancer.

Citation Format: Humberto Parada, Xuezheng Sun, Chiu-Kit Tse, Lawrence S. Engel, Andrew F. Olshan, Melissa A. Troester. Plasma levels of polychlorinated biphenyls (PCBs) and breast cancer mortality: The Carolina Breast Cancer Study [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr D095.