This is a hotly debated issue. While there are no definitive studies linking occupational, environmental, or chemical exposures to breast cancer risk, there is a mounting body of evidence suggesting that there may be. Exposure to the pesticide DDT is thought to increase the risk of breast cancer because its breakdown products mimic the effects of estrogen on the body. Prolonged estrogen exposure is a known risk factor for breast cancer. Consumption of animals that have been injected with hormones (including estrogen) to speed their growth may also be a risk factor.