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ve t p ffe d l e ec at preparations (POPs) including the levonorgestrel-releasing intrauterine system (LNG-IUS) are still gens block this effect. As a result of progestogen sia and changes in proliferative status. They induce transformation of stromal fibroblasts; these terminal-differentiated cells can no longer proliferate and are, secretory, in gland-very potent.g. cribiform cellularity, mor-)angio-logic atypia; Most, if not all, of these effects, which are still a uggest that the risk of sal relation-not ethical in the field of contraception. Thus, the aim Endocrine-Related Cancer (2010) 17 R263–R271However, many more changes in histologicalpublished more than 15 years ago.features occur during hormonal contraceptionshed in withdrawal bleeding (if implantation does not occur), with important differences dependent on the pharmacology of the progestogens used (type, dosage, pharmacokinetics, etc). of this systematic review was to search for observa-tional studies with a focus on case–control and cohort studies and to summarize the results, especially those of the most important (large) studies. To our know-ledge, the last systematic review on this topic wasglandular epithelial secretory activity and decidual ship in clinical studies would require randomized placebo-controlled interventional studies, which areexposure to estrogen levels (as in the luteal phase). Progestogens protect from estrogen-induced hyperpla-topic of important ongoing research, s hormonal contraceptives can reduce endometrial cancer. To demonstrate a cauaction, cell proliferation ceases, despite continuousstimulates endometrial cell division, whereas progesto- the latter are powerful markers and predictors for progestogenic potency.reduce endometrial hyperplasia but should only be used in exceptional cases in patients with or after endometrial cancer. In contrast to nonhormonal IUS, systemic side effects cannot be excluded with LNG-IUS, but they are certainly rare, as the main effect has decreased the endometrial estrogen response because of the high endometrial tissue levels of LNG. Endocrine-Related Cancer (2010) 17 R263–R271