Reproductive history influences breast cancer risk but the cellular mechanisms are unclear. Here it is shown that ovarian hormones regulate the size of the mammary stem cell pool in mice. The size of this pool increases when progesterone levels increase during the reproductive cycle. Progesterone probably regulates stem cell numbers through a paracrine mechanism involving induction of RANKL and Wnt in luminal cells.
- Purna A. Joshi
- Hartland W. Jackson
- Rama Khokha
