Abortion Drug RU-486 vs. Breast Cancer

The abortion drug RU-486 prevents breast cancer in mice carrying a dangerous "cancer gene" mutation, new studies show.

RU-486 itself will not be the answer for women; the potent drug is not meant for long-term uses such as cancer prevention.

But scientists say the cancer-preventing effects of RU-486 stem from the drug's ability to block progesterone, a major sex hormone.

So new, safer progesterone-blocking drugs are on the way to treat women with the BRCA1 gene mutations linked to breast cancer, says Eva Y.-H. P. Lee, PhD, professor of biological chemistry and cell biology at the University of California, Irvine.

"To prevent cancer, many women who are BRCA1 carriers have very traumatic surgery -- their ovaries and both breasts are removed," Lee tells WebMD.

"Many of these women have asked us about clinical use of RU-486, but it would have too many side effects for prevention use," she says. "However, I am happy to say that for the past three years there have been companies working on more appropriate anti-progesterone drugs."

Lee and colleagues report their findings in the Dec. 1 issue of Science.

How BRCA1 Causes Cancer

Breast cancer strikes between 36% and 85% of women with mutations in the BRCA1 gene, or in a second gene, BRCA2. These women also face a 16% to 60% chance of ovarian cancer.

Every cell in the body carries BRCA1 genes, which are involved in DNA repair.

It has never been clear why mutant, inactive versions of the gene are linked mostly to breast and ovarian cancer.

Lee's team found that mouse and human breast cells with BRCA1 mutations are overly sensitive to progesterone, a major sex hormone. Indeed, mice with BRCA1 mutations get breast cancer.

But when Lee and colleagues gave the mice RU-486, the animals did not get the cancer.

The researchers are now testing new progesterone-blocking drugs to see if they have the same effect in mice.

These are exciting findings.

But researchers can cure many kinds of cancers in mice, notes Kristin A. Skinner, MD, director of the multidisciplinary breast program and chief of surgical oncology at the University of Rochester in New York.

"This study shows progesterone blockage prevented breast cancer in a very special group of mice -- mice that carried mutations not just in the BRCA1 gene but in the p53 cancer gene as well," Skinner tells WebMD. "And what happens in mice is not always what happens in humans."

Still, Skinner is impressed with the new insights Lee's team has provided into how BRCA1 mutations lead to breast cancer.

"But this is a far cry from proving we can prevent these cancers by using an anti-progesterone like RU-486," she says.

"Before that happens," Skinner says, "we have to look at how RU-486 impacts normal human breast cells, how it affects breast cells with BRCA1-only mutations, and how it affects ovary cells ... because the biggest threat to life for women with BRCA1 mutations is ovarian cancer, not breast cancer."

SOURCES: Poole, A. Science, Dec. 1, 2006; vol 314: pp 1467-1470. Eva Y.-H. P. Lee, PhD, professor of biological chemistry and developmental and cell biology, University of California, Irvine. Kristin A. Skinner, MD, chief, surgical oncology and director, multidisciplinary breast program, University of Rochester, N.Y. National Cancer Institute.