Authors: Santos SJ, Aupperlee MD, Xie J, Durairaj S, Miksicek R, Conrad SE, Leipprandt JR, Tan YS, Schwartz RC, Haslam SZ.
Publication Year: 2009
Citation: J Steroid Biochem Mol Biol. 2009;115(3-5):161-72.
This experimental study used breast cells from mice, cultured in vitro. First, the behavior of the cells was compared after exposure to either progesterone or the synthetic progestin, promogestone. After seeing similar proliferation with both progestogens, they then went on to conduct gene expression studies (again in the mouse mammary cells) using only the promogestone. They found that certain genes were activated by the promogestone, and these were regulated by progesterone receptor A, which is increased relative to progesterone receptor B in more aggressive breast cancers in humans. The researchers imply that the expression of these genes in the cultured mouse breast cells may translate to growth-promoting actions of progesterone in the breast tissue in humans. However, human tissue was not studied here, and the mouse cells under investigation were in an environment very different to that under which they would be growing in the intact mouse. Any conclusions regarding the possibility that progesterone in itself could promote breast cancer in a living human can, therefore, not be inferred from this study. In addition, synthetic progestins are already known to have very different actions to those of progesterone itself in clinical studies. Progesterone has not been shown to cause or exacerbate breast cancer in women; on the contrary, it has been found in clinical studies to be associated with a lower breast cancer risk.