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Abortion Pill Blocks Breast Cancer In Mice


IRVINE, Calif. -- The chemical compound at the heart of the so-called abortion pill also appears to block breast cancer, at least in experimental mice.

IRVINE, Calif., Nov. 30 -- The chemical compound at the heart of the so-called abortion pill also appears to block breast cancer, at least in experimental mice.

In mice genetically engineered to carry mutations in two genes involved in most human breast cancers, Mifeprex (mifepristone) completely blocked tumor development. No palpable tumors were detected at 12 months of age, according to Eva Lee, Ph.D., of the University of California at Irvine.

By contrast, the median time to development of a palpable tumor in untreated and placebo-treated mice was 6.6 months and all the animals came down with the disease by at least 8.7 months of age, Dr. Lee and colleagues reported in the Dec. 1 issue of Science.

"We're excited about this discovery and hope it leads to new options for women with a high risk for developing breast cancer," Dr. Lee said in a statement.

The finding arose from experiments aimed at understanding the relationship of progesterone to the normal BRCA1 gene, which when mutated predisposes women to breast and ovarian cancer.

Mice genetically engineered to lack both a functional BRCA1 gene and p53 gene (another tumor suppressor gene that is commonly mutated in women with breast cancer) were chosen to mimic human breast cancer.

In those double-knockout mice, the researchers found, the breast tissue resembled that of wild-type pregnant mice, even though they had not become pregnant, suggesting that the proliferation of mammary epithelial cells was altered.

The mammary glands of the mice showed sharply increased ductal branching and alveolar proliferation, compared with wild-type mice, the researchers said.

Such proliferation is known to be driven by the ovarian hormones, estrogen and progesterone, and indeed the researchers found a strong mitogenic effect when they treated the double knock-out mice with estrogen, progesterone, or both.

However, Dr. Lee and colleagues reported, mammary epithelial cells in the mice had significantly more progesterone receptors than similar cells from control mice, while showing no difference in estrogen receptors.

The increase in receptors implies "that progesterone plays a role in the development of breast cancer by encouraging the proliferation of mammary cells that carry a breast cancer gene," Dr. Lee said.

Progesterone is essential to the development of a pregnancy, which is why Mifeprex - which blocks the progesterone receptor - is used as an abortion pill, the researchers noted.

In the double-knockout mice, administration of the compound - in a 60-day time-release pellet -- decreased the ductal branching and alveolar proliferation seen in the untreated animals, Dr. Lee and colleagues reported.

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