No chemical in the environment has ever credibly been associated with breast cancer risk.
The chief of Breast Cancer Action writes at the Huffington Post:
Fracking involves injecting millions of gallons of water mixed with tens of thousands of gallons of chemicals at extreme pressure to break up rock formations and release natural gas. Approximately 40,000 gallons of chemicals — many of which are known to harm human health — are used each time a well is fracked. Around 700 chemicals are routinely used in the process of drilling and fracking, many of which are not disclosed by fracking companies; and many of which are associated with a host of diseases and disorders ranging from respiratory illnesses and reproductive problems to cancers, including breast cancer.