Progesterone inhibits human breast cancer cell growth through transcriptional upregulation of the cyclin‐dependent kinase inhibitor p27Kip1 gene

Abstract
The effects of progesterone derivatives on breast cancer development are still controversial, probably accounting for their biphasic, opposed effects on mammary cell‐cycle regulation. Here, we demonstrate in vitro that the growth‐inhibitory effects of progesterone on breast cancer T‐47D cells require the transcriptional upregulation of the cyclin‐dependent kinase inhibitor p27Kip1 (p27) gene. A statistical analysis of human tumor biopsies further indicates that p27 mRNA levels correlate to progesterone receptor (PR) levels. Moreover, p27 gene expression is inversely associated with tumor aggressiveness, and is a prognostic factor of favorable disease outcome. Thus, progesterone derivatives selectively activating the p27 gene promoter could be promising drugs against breast cancer progression.