AR and breast carcinoma: Additionally, although synthetic progestins clearly closely mimic progesterone in vitro, some synthetic progestins (medroxyprogesterone acetate) may alter androgen receptor (AR) [24] or glucocorticoid receptor (GR) [25] signaling, exhibit different half-lives, and are metabolized differently than natural progesterone, and therefore may be associated with different breast cancer risks relative to their naturally occurring counterparts [26,27].