Established breast cancer risk factors, such as hormone replacement therapy and reproductive history, are thought to act by increasing estrogen and progesterone activity. Researchers at the Silent Spring Institute reviewed 2000 chemicals registered with the EPA, and found 296 chemicals that caused an increase in levels of estradiol, which is a form of estrogen and the major female sex hormone, progesterone levels, or both estradiol and progesterone in adrenal cell culture.
Of these chemicals, 71 caused an increase in both hormones. They included chemical flame retardants, dyes, fungicides, and pesticides.
The findings suggest that some of these synthetic chemicals could increase the risk of breast cancer by way of stimulating the two hormones linked to breast cancer: estrogen and progesterone.
Read more about the study here.