Abstract
Breast cancer is the main risk associated with menopause hormone therapy (MHT). It is a hormone-dependent cancer. In postmenopausal women, about 80% of cases are estradiol receptor-positive. In cohort studies only estradiol receptor-positive breast cancers are promoted by MHT. Different levels of risk with estrogen-only treatment and combined treatment with estrogen + progestin are shown in randomized trials and observational studies. Several non-randomized studies show a lower risk with progesterone and retroprogesterone than with synthetic progestins. Progesterone and progestin are non-selective ligands for the progesterone receptor and bind also with other steroid receptors, with agonistic or antagonistic effects according to the structure of the molecule. Their half-life and metabolism are also different, progesterone being rapidly degraded with a short half-life. These aspects will be discussed in this review.
Conflict of interest
The authors report no conflict of interest. The authors alone are responsible for the content and writing of this paper.