The experiment does not espouse using the drug this way but shows how the breast cancer gene BRCA1 functions by developing a hormone called progesterone which RU-486 blocks.
"All of us have to be cautious," said cell biologist Eva Lee of the University of California, Irvine, who led the research. "But I do think if there is a better anti-progesterone available, hopefully there will be other options in the future for these women."
Cancer specialists have lauded the experiment although they warn women not to expect too much yet.
"This is an avenue worth pursuing on a research level," said Dr. Claudine Isaacs, an oncologist at Georgetown University Hospital.
"This is work in a mouse," she said. "It's clearly too early to start recommending use of this agent."
Dr. Len Lichtenfeld, the American Cancer Society's deputy chief medical officer, said researchers and patients will "take interest in this topic and explore it further."
He said it was "elegant research," but stressed that "it would not be appropriate in any way, shape or form that women start taking RU-486 for this purpose."
When used for a long time RU-486 may suppress the immune system and cause side effects.
