Studies were not available that evaluate the risk of breast cancer in women exposed to simazine. Simazine does not cause breast tumors in mice. One study has reported a significant increase in the incidence of malignant and benign breast tumors in one strain of female rats fed high levels of simazine for long periods of time, compared to rats that did not receive a diet that contained simazine. It should be noted that the high levels of simazine used in this study are much higher than levels that people would be exposed to from food, water, soil, or through occupational exposures to this herbicide. Researchers are investigating whether simazine changes the levels of hormones in experimental animals in a way that may affect breast tumor formation.
Hormones are chemical messengers in the body.
Some researchers have suggested that exposure to the hormone estrogen can affect breast cancer risk. Simazine-treated animals did not have elevated levels of estrogen in their blood. However, they did have elevated levels of another hormone called prolactin, and this hormone is known to play a role in the development of breast tumors in laboratory animals. Most researchers believe that prolactin does not play a significant role in human breast cancer. There is currently no evidence that simazine can affect breast cancer risk in other ways.