This is a hotly debated issue. Although there are few definitive studies demonstrating that occupational, environmental, or chemical exposures increase breast cancer risk, there is a mounting body of evidence suggesting that there may be a link.
Prolonged estrogen exposure is a known risk factor for breast cancer. Exposure to the pesticide DDT is thought to increase the risk of breast cancer, because its breakdown products mimic the effects of estrogen in the body. Consumption of food from animals that have been injected with hormones (including estrogen) to speed their growth also may be a risk factor.