State of the evidence 2017: an update on the connection between breast cancer and the environment

Abstract

Background: In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer. Singly and in combination, these toxicants may have contributed significantly to the increasing rates of breast cancer observed over the past several decades. Exposures early in development from gestation through adolescence and early adulthood are particularly of concern as they re-shape the program of genetic, epigenetic and physiological processes in the developing mammary system, leading to an increased risk for developing breast cancer. In the 8 years since we last published a comprehensive review of the relevant literature, hundreds of new papers have appeared supporting this link, and in this update, the evidence on this topic is more extensive and of better quality than that previously available.

Conclusion: Increasing evidence from epidemiological studies, as well as a better understanding of mechanisms linking toxicants with development of breast cancer, all reinforce the conclusion that exposures to these substances - many of which are found in common, everyday products and byproducts - may lead to increased risk of developing breast cancer. Moving forward, attention to methodological limitations, especially in relevant epidemiological and animal models, will need to be addressed to allow clearer and more direct connections to be evaluated.

Keywords: Bisphenol a; Breast cancer; Endocrine disrupting compounds; Environmental toxicants; Light-at-night; Radiation.

Fig. 1

Complexity of factors affecting risk for developing breast cancer. This synopsis of much of the evidence described in this report demonstrates the complexities of the potential connections between exposures to environmental toxicants and development of breast cancer, all embedded in a web-like framework of interconnected factors. Solid arrows indicated connections that have been demonstrated directly between exposures and breast cancer risk, or, as appropriate, mediated through factors described in the framing section of this review. These relationships reflect results of the combined human epidemiological and/or animal studies discussed. Dashed arrows indicate connections between exposures and risk for breast cancer that are more ambiguous, with evidence coming from non-human or -animal studies, but without the in vivo data to support more directly the link. Arrows are not weighted to indicate relative strength of links. Rather the purpose of this model is to demonstrate the complexity of the relationships between environmental factors and breast cancer. (Updated and modified from Gray et al. 2009 [11])