Abortion Pill May Help Prevent Breast Cancer

Mouse study shows that RU486, or compounds like it, might have promise

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By Amanda Gardner
HealthDay Reporter

THURSDAY, Nov. 30, 2006 (HealthDay News) -- The abortion pill might ward off breast cancer in women at high risk for the disease.

New research finds the chemical compound in RU486 prevented tumors from growing in mice that were genetically engineered to carry the BRCA1 breast cancer gene.

RU486, or mifepristone, blocks the production of the hormone progesterone, and this anti-progesterone effect could have prevented the growth of tumors in these mice, the authors speculated. RU486 aborts a pregnancy via the same mechanism.

Still, all this is a far cry from recommending RU486 as breast cancer therapy in people, experts cautioned.

"It's an interesting observation," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System, in Baton Rouge, La. "It's basically showing that this particular agent can change some of the mammary function, but it's a real leap to say that it may be useful in cancer prevention."

The study appears in the Dec. 1 issue of Science.

Genes can greatly influence breast cancer risk. Experts have long known that women with mutations in the BRCA1 gene are at a much higher risk of developing both breast and ovarian cancer. The mutations mainly affect hormone-responsive tissues, although experts have been unclear as to why.

For this study, researchers studied mice that carried the mutated form of BRCA1, causing them to be highly susceptible to breast cancer.

As it turned out, the mice's mammary epithelial cells accumulated high levels of progesterone receptors and then divided and proliferated at an abnormally rapid rate.

However, Mice treated with RU486 did not develop breast tumors by the time they reached 1 year of age. On the other hand, untreated mice developed tumors by eight months.

Progesterone may encourage the proliferation of mammary cells that carry a breast cancer gene, the researchers said.

Although the study was done in mice, the same mechanism occurs in human cells, said study author Eva Lee, a professor of developmental and cell biology and biological chemistry at the University of California, Irvine.

She speculated that clinicians may one day be able to use progesterone-blocking compounds to prevent breast cancer in women with a genetic predisposition.

But RU486 may not be the best candidate, however.

"It is the most widely available anti-progesterone drug," Lee said. "We are currently testing a more specific anti-progesterone drug to see whether it has the same effect and if that's proven, we'll go to a small clinical trial to see if that anti-progesterone is effective in a high-risk population."

More information

Learn more about breast cancer at the U.S. National Cancer Institute.

SOURCES: Eva Lee, Ph.D., professor, developmental and cell biology and biological chemistry, University of California, Irvine; Jay Brooks, M.D., chairman, hematology/oncology, Ochsner Clinic Foundation, Baton Rouge; Dec. 1, 2006, Science

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