Published in today's online version of Nature Medicine, researchers at the Lombardi Cancer Center at Georgetown University studied cadmium and its uncanny ability to mimic estrogen's effects on the body. When exposed to low doses of cadmium, female rats show an increase in mammary gland density and uterine weight, and changes in the endometrial lining, all telltale developments in the early onset of breast cancer.
Additionally, when pregnant rats were exposed to the same low dose, their female offspring experienced earlier onset of puberty and mammary gland development. Early onset of puberty can increase a woman's chance for getting cancer by fifty percent.
"We never expected to see this strong a relationship, given how different the cadmium and estrogen compounds are," said Mary Beth Martin, Ph.D., associate professor of oncology at Georgetown University Medical Center. "Cadmium's ability to functionally mimic estrogen and its affect on cell growth is quite remarkable. What we saw suggests a direct link between low dose cadmium exposure and increased risk for breast cancer."
Estrogens are a family of steroidal hormones that are synthesized in a variety of tissues but are primarily produced in the ovaries during reproductive years. One of the main functions of estrogens is to promote the growth and differentiation of the sexual organs and other tissues related to reproduction. The biological effects of estrogens are mediated by estrogen receptors alpha and beta; molecules that bind to and activate these receptors may pose health risks.
In this study, Martin and her colleagues exposed ovariectomized rats to levels of cadmium comparable to the provisional tolerable weekly dietary intake recommended by the World Health Organization. The cadmium bound to and activated estrogen receptors, mimicking potentially dangerous estrogenic activity.
Cadmium is a naturally occurring metal, found in soil, rocks, and water. It has well known carcinogenic effects, with documented links between cadmium exposure and lung cancer, lung disease, and kidney damage. Additional studies have suggested a link to prostate cancer. People are exposed to cadmium by eating food grown in contaminated soil or fish from tainted water, but more extreme exposure comes from smoking or interaction with smelting, welding or shipbuilding. Smoking doubles the average daily intake of cadmium.
"There is great concern about what is an acceptable level of environmental exposure to certain carcinogens, and how do those exposures affect our risk for getting cancer," said Martin. "The more we learn about how this works in rats and eventually people, the better lifestyle choices women can make."
The Lombardi Cancer Center, part of Georgetown University Medical Center and Georgetown University Hospital, seeks to improve the diagnosis, treatment, and prevention of cancer through innovative basic and clinical research, patient care, community education and outreach, and the training of cancer specialists of the future. Lombardi is one of only 39 comprehensive cancer centers in the nation, as designated by the National Cancer Institute, and the only one in the Washington DC area. For more information, go to http://www.georgetown.edu/gumc.
Journal
Nature Medicine