Chemical Triggers Breast Cancer

The chemical, 4-nonylphenol (4-NP), is released into the environment from plastics, cleaning materials, textiles, and some paper. The chemical has also been found in drinking water and some processed foods. It stimulates an enzyme system in the liver that increases the production of estriol, a hormone associated with breast cancer. The chemical's affinity for estrogen receptors in breast tissue is 4,000 times less than that of estrogen.

In comparing the effects of various doses of 4-NP and estrogen on mice, researchers discovered that while 4-NP stimulates estriol metabolism in the liver, it does not lead to increased levels of estriol in the bloodstream. They concluded that as well as stimulating enzymes that produce estriol, 4-NP also has a direct inhibiting effect on estriol production. In a second experiment, the researchers gave doses of 4-NP to mice genetically engineered to readily develop breast cancer. Over a 32-week period, many of these mice developed breast cancer. Those given equivalent doses of estrogen, based on the relative binding affinities of 4-NP and estradiol for their receptors, did not develop mammary cancer.

"Long term exposure to 4-nonylphenol could leave individuals at a significantly increased risk of developing breast cancer,” concluded toxicologist William Baldwin, from the University of Texas, El Paso (USA), a member of the research team. The findings were reported in the July 12, 2005, online edition of the Journal of Applied Toxicology (Wiley InterScience).