Exposure to the environmental estrogen 4-nonylphenol increases the risk of breast cancer in mice, according to a new report.

This research is another example demonstrating that estrogen-like chemicals in the environment “have the ability to cause cancer,” said Dr. William S. Baldwin from University of Texas at El Paso. “Whether they really do or not is unknown.” The animals’ exposure in this study was much higher than that encountered in the environment.

Breast cancer is the most commonly diagnosed cancer in women and environmental factors appear to cause many of these cases. Many of the environmental factors increase a woman’s level of the female hormone estrogen, which is thought to be a major contributing factor to the disease.

In the Journal of Applied Toxicology, Baldwin and colleagues explain that 4-nonylphenol is released from cleaning agents, textiles, paper, plastic, personal care products and agricultural chemicals.

The team investigated the effects of 4-nonylphenol on the incidence of breast cancer in mice susceptible to the disease.

All five mice treated with 4-nonylphenol formed breast tumors, the researchers report, whereas one mouse in the control group and no mice treated with the female hormone estradiol formed breast tumors.

Treatment with 4-nonylphenol also shortened the latency period before mammary tumor development and increased the likelihood that breast tumors would spread to the lung.

Baldwin cautioned that the doses of 4-nonylphenol given to the mice are “much greater than what humans are exposed to on a daily basis.” He estimated the dose at 1000 times the level of human exposure.

Baldwin and his colleagues plan to continue their investigations by looking into the effects of developmental exposures of nonylphenol on breast cancer.

SOURCE: Journal of Applied Toxicology July/August 2005.