Effect of PCBs in plasma on risk of postmenopausal breast cancer

Abstract

Background: Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants suspected to cause negative health effects such as cancer. However, the findings on breast cancer are inconsistent, and lack data on larger populations. The objective in this master thesis is to study the association between estimated plasma concentration of summed PCBs and the incidence of postmenopausal breast cancer overall, as well as hormonal receptor positive and negative postmenopausal breast cancer.

Methods: I used data from 48,675 participants in the population-based Norwegian Women and Cancer cohort and predicted summed PCB concentrations from a previously developed linear regression model. Participants were afterwards categorized into tertiles of low, medium, and high levels of summed PCBs. Multivariable Cox proportional hazard regression was used to assess the association between PCB exposure and incidence of postmenopausal breast cancer, including selected subtypes.

Results: I found significant associations between higher predicted plasma concentrations of summed PCBs and the incidence of postmenopausal breast cancer (Moderate vs low: HR = 1.09, 95 % CI: 0.97-1.23, high vs low: HR = 1.22, 95 % CI: 1.08-1.38, p trend < 0.01), including ER+ (Moderate vs low: HR = 1.01, 95 % CI: 0.97-1.25, high vs low: HR = 1.18, 95 % CI: 1.04-1.35, p trend = 0.013) and PR+ (Moderate vs low: HR = 1.20, 95 % CI: 0.97- 1.47, high vs low: HR = 1.27, 95 % CI: 1.02-1.57, p trend = 0.036) subtypes. No association was found when assessing ER- and PR- postmenopausal breast cancer (ptrend ER- = 0.627, ptrend PR- = 0.580).

Conclusion: Higher predicted plasma concentrations of summed PCB increase the risk of postmenopausal breast cancer, ER+ and PR+ postmenopausal breast cancer, but not ER- and PR- postmenopausal breast cancer.