Figure 2. Progesterone‐driven cellular and molecular changes in the mammary gland.

(A) The murine estrous cycle is shown with mammary whole mounts depicting the gross morphological changes elicited by fluctuations in the ovarian hormones, estrogen, and progesterone. The corresponding expansion in mammary stem and progenitors is also highlighted. Schematic illustrates the strategy of utilizing factors that limit stem/progenitor expansion as chemopreventive agents in breast cancer. Ulipristal acetate is a selective progesterone receptor modulator, and denosumab is an anti‐RANKL agent. (B) Schematic of key mitogenic paracrine effectors downstream of progesterone in the breast, some of which may prove effective as targets in future breast cancer chemoprevention strategies.