Biological effects of progestins in breast cancer

The action of progestins is derived from many factors: structure, affinity for the progesterone receptor or for other steroid receptors, the target tissue considered, the biological response, the experimental conditions, the dose and metabolic transformation. The proliferative response to progestins in human breast cancer cells is contradictory: some progestins inhibit, others stimulate, have no effect at all, or have a dual action. For instance, medroxyprogesterone acetate has a stimulatory effect on breast cancer cells after a short period of treatment, but this effect becomes inhibitory when treatment is prolonged. It has been demonstrated that, in hormone-dependent breast cancer cells, various progestins (nomegestrol acetate, medrogestone, promegestone) are potent sulfatase inhibitory agents. The progestins can also involve the inhibition of the mRNA expression of this enzyme. In another series of studies it was also demonstrated that some progestins are very active in inhibiting 17beta-hydroxysteroid dehydrogenase for the conversion of estrone to estradiol. More recently it was observed that the progestins promegestone and medrogestone stimulate sulfotransferase for the formation of estrogen sulfates. Consequently, the action of progestins in blocking estradiol formation via sulfatase, or in stimulating the effect on sulfotransferase activity, can open interesting and new possibilities in clinical applications in breast cancer.