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Mifepristone Prevents Breast Cancer in Animal Study

Progesterone antagonist prevents tumors in BRCA1-deficient mice

THURSDAY, Nov. 30 (HealthDay News) -- A progesterone antagonist such as mifepristone can prevent breast cancers in mice with a deletion of the BRCA1 breast cancer susceptibility gene, according to the results of a study published in the Dec. 1 issue of Science.

To examine the role of estrogen and progesterone receptors in BRCA1-mediated tumorigenesis, Eva Y.-H.P. Lee, Ph.D., and colleagues from the University of California in Irvine used mice with deletions in BRCA1 and another tumor suppressor gene.

The researchers found that the mammary glands of the mice accumulated lateral branches and underwent alveologenesis, similar to pregnant normal mice. The mutant mammary epithelial cells expressed high levels of progesterone receptors, and treating the mice with mifepristone prevented breast cancer development. Treated mice did not develop palpable tumors after 12 months, while tumors developed after five to nine months in control mice.

"These findings reveal a tissue-specific function for the BRCA1 protein and raise the possibility that anti-progesterone treatment may be useful for breast cancer prevention in individuals with BRCA1 mutations," Lee and colleagues conclude.

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