Mifepristone or RU-486 blocks the sex-hormone, progesterone, which causes cancer cells to proliferate.
The study published in Science suggest that the mechanism could be most effective on women who have a genetic inclination to cancers.
Statistics reveal, women over the age of 70, with a faulty BRCA1 gene develop breast or ovarian cancer.
The findings were part of a study done on mice by Professor Eva Lee from the University of California at Irvine. She and her colleagues studied genetically engineered mice lacking the gene key gene BRCA1.
Dr. Kat Arney from Cancer Research UK told BBC news: "This is an interesting discovery, which could one day help prevent breast cancer," adding, "We already know that sex hormone levels can have a big impact on breast cancer risk, and can fuel the growth of some breast cancers."
Arney explained, "These new results tell us a lot about the way that flaws in the BRCA1 gene may lead to breast cancer, by making faulty breast cells more responsive to progesterone."
Lee told the AP, ''All of us have to be cautious...'But I do think if there is a better anti-progesterone available, hopefully there will be other options in the future for these women.''
