Progestins and cancer

The role of progestins in breast tissue is less well defined than in the endometrium. Although in vitro studies have shown that progestins induce a similar decrease in both estrogen and progesterone receptors and an increase in 17β-estradiol dehydrogenase in the breast as in the endometrium ,epidemiologic studies have suggested that progestins prevent endometrial cancer ,but do not reverse the estrogen-related increase in breast cancer risk in long-term hormone-replacement therapy (HRT). Other studies have also suggested a protective effect for progestins on breast tissue. The dual effect of progesterone and progestins on the cell cycle has been demonstrated ,suggesting that according to the duration of administration ,the same steroid can induce cells to enter the multiplication phase or to enter a resting state. Progestins exert different effects according to the steroid from which they are derived ,e.g. pregnanes derived from progesterone ,estranes or gonanes derived from testosterone. Some estrane der...