Estrogen and progesterone promote the proliferation and activity of mouse mammary stem cells, according to new research published online today (April 11) at Nature -- possibly explaining the link between exposure to the hormones and breast cancer.
Microphotography of a preparation
of a healthy mammary gland

Image: Wikimedia commons,
linkurl:Luis A. Pardo et al.;
"It's a pretty good paper," said linkurl:John Stingl,; a researcher at the Cancer Research UK Cambridge Research Institute, who did not participate in the study. In a very direct way, the researchers have successfully measured the effects of progesterone and estrogen on mammary stem cells, he said. Estrogen and progesterone levels have profound effects on breast development and breast cancer risk. There is a clear correlation between number of menstrual cycles (and thus lifetime exposure to these hormones) and breast cancer risk, for example, and therapeutic regimens that inhibit the binding or synthesis of estrogen reduce...

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