Since its discovery in 1994, the BRCA1 gene has given up its secrets grudgingly. Early on, scientists recognized that it kept cancer at bay. Women carrying a mutation in the gene face an extremely high risk of breast and ovarian cancer. Researchers have struggled to understand how the protein encoded by a normal BRCA1 gene works.
A study in mice now suggests one possibility: The BRCA1 protein moderates the hormone progesterone's effect in breast cells. The protein appears to calm those cells when progesterone urges them to divide and grow.
Earlier research had shown that BRCA1 protein orchestrates the repair of damaged DNA. But since that process occurs continuously in every cell throughout the body, the finding failed to explain how a mutated BRCA1 would predispose a woman specifically to cancers of the breasts or ovaries.