Chickens Studied for Ways to Prevent and Detect Ovarian Cancer

Division of Cancer Prevention

Ovarian cancer is known as the “silent killer,” because researchers have been unable to develop a test or screening tool to reliably detect it in the early, more treatable stages. There has also been little progress on prevention of the disease. Dale Buchanan Hales, Ph.D., chair of the Physiology Department at Southern Illinois University School of Medicine, is trying to find ways to prevent or detect the disease sooner.

With NCI funding*, Dr. Hales is continuing his research using Gallus domesticus or the common American chicken. Since publication of a landmark paper in 1971, the study of ovarian cancer has benefited from this unusual animal model, said Dr. Hales, because chickens develop a lot of spontaneous ovarian cancer, even more than humans.

Most scientists believe this higher risk of ovarian cancer in domesticated chickens can be explained by the incessant ovulation hypothesis. “In an effort to maximize their egg production, farmers breed them to ovulate about five days out of seven,” Dr. Hales explained. “With each ovulation comes inflammation and oxidative stress to the cells of the ovarian surface epithelium (OSE), which is where ovarian cancers develop in hens and women.” Over just a few years of reproductive life, chicken hens ovulate up to 500 times, which is comparable to the number of times women ovulate over 30-40 years.

“Women have about four weeks to recover from the oxidative stress and inflammation of each cycle, while the chicken must endure a chronic higher inflammatory load,” Dr. Hales commented. “I’m pretty sure this explains chickens’ high rate of ovarian cancer.”

Based on previous research in breast cancer, Dr. Hales believes that ovarian cancer is also driven by both estrogen and cyclooxygenase-1 (COX-1) that can fuel OSE carcinogenesis by producing too much prostaglandin. This hormone and enzyme are essential to ovarian function at normal levels, but when overproduced, they can fuel unwanted cell growth.

Researchers have known for years that fruits and vegetables – in particular, cruciferous vegetables such as cauliflower, cabbage, broccoli, and Brussels sprouts – can impede or prevent some cancers from developing in animals. Dr. Hales’ laboratory is testing whether two compounds, found naturally in broccoli, can interfere with OSE carcinogenesis in chickens. The first compound sulforaphane is an antioxidant that affects many steps in the development of cancer, but it cannot be easily produced synthetically so plant extracts are the primary source.

“Testing dietary strategies always presents a challenge, because the amount of activity can vary significantly from plant to plant,” Dr. Hales noted. He works with the University of Illinois, which is producing broccoli under strict growth conditions and freeze dries the plants to get rid of the 90 percent water content. “This gives us a pretty reliable source of sulforaphane,” he added.

The second compound, indole-3-carbinol (I3C), is another phytoactive ingredient in broccoli, which can be produced synthetically. “It has been studied extensively, and we know it increases production of enzymes that affect the estrogen metabolism process, and some that also eliminate some carcinogens from the system,” Dr. Hales explained.

The researchers are feeding hens broccoli-based diets enriched with these two ingredients and are testing whether either compound alone, or the two together, has an impact on ovarian cancer. Then the researchers will wait to see which hens will develop ovarian cancer spontaneously. Dr. Hales and his colleagues also plan to develop ways to look at cells in the hens’ OSE as they begin to mutate from normal to carcinogenic.

Because the chicken model of ovarian cancer is close to the human model of ovarian cancer, the tests that researchers are trying to develop might lead to creation of a cancer screening tool that could be used to look for early signs of ovarian cancer in the blood or urine of women “Ovarian cancer is not nearly as lethal when we catch it early, and we really need a better way to do that,” Dr. Hales said.