In the United States, breast cancer is the most common invasive malignancy and the second most common cause of death from cancer in women. Reproductive factors, estrogen, and progesterone have major causal roles, but concerns about other potential causes in the external environment continue to drive research inquiries and stimulate calls for action at the policy level. The environment is defined as anything that is not genetic and includes social, built, and chemical toxicant aspects. This review covers the scope of known and suspected environmental factors that have been associated with breast cancer and illustrates how epidemiology, toxicology, and mechanistic studies work together to create the full picture of environmental effects on this malignancy. Newer approaches to risk-related evaluations may allow this field to move forward and more clearly delineate actionable environmental causes of this most common of cancers in women.
Keywords: chemical toxicants; disrupting chemicals; endocrine; epidemiology; social determinants; toxicology.