Environmental estrogen-like chemical is potent trigger for breast cancer

New research published in the latest issue of the Journal of Applied Toxicology, shows that in experimental mice an estrogen-mimicking chemical, 4-nonylphenol, triggers breast cancer to a greater extent than naturally occurring estrogens based on their relative affinity for the estrogen receptor. 4-Nonylphenol is released into the environment from cleaning materials, textiles, plastics and some paper.

Breast cancer is the most commonly diagnosed cancer in women and environmental factors appear to cause about three-quarters of cases. Many of the environmental factors increase a woman’s levels of the hormone estrogen, which is thought to be a major contributing factor in the disease.

4-Nonylphenol mimics estrogen and is found in the environment, and researchers in the past have found it in drinking water and in some processed foods. In the liver it stimulates an enzyme system that in turn increases the production of estriol, a hormone associated with breast cancer. It also has an affinity for estrogen receptors in breast tissue that trigger growth, and this affinity is 4,000 times less than estrogens.

To assess its ability to cause breast cancer, a team of researchers at the University of Texas at El Paso and Clemson University in Southern Carolina, compared the effect of giving various doses of 4-nonylphenol and estrogen to mice.

In one set of experiments, they discovered that while 4-NP indeed stimulates estriol metabolism in the liver, it doesn’t lead to increased levels of estriol in the blood stream. The researchers conclude that as well as stimulating enzymes that in turn produce estriol, it must also have a direct inhibiting affect on estriol production.

In a second set of experiments, they gave a variety of doses of 4-NP or estrogen to mice that are genetically engineered to readily develop breast cancer. Monitoring them over 32 weeks, the researchers found that many of the mice given 4-NP developed breast cancer. Those given equivalent doses of estrogen based on the relative binding affinities of nonylphenol and estradiol for their receptor, did not develop mammary cancer.

“Long term exposure to 4-nonylphenol could leave individuals at a significantly increased risk of developing breast cancer,” says toxicologist William Baldwin, from the University of Texas at El Paso.