Hormone replacement therapy (HRT) remains the most effective treatment for menopausal symptoms and has been shown to prevent bone loss and fracture. The progestogen is added to provide endometrial protection in women with an intact uterus. After the publication of the initial WHI (Women’s Health Initiative) results in 2002 reporting an overall increased risk of breast cancer, many women discontinued HRT. Despite the re-analysis of the results by subgroups of patients and updates with extended follow-up, much controversy remains, which we will analyze later in the text. Different types of estrogen or progestogen, as well as different formulations, doses, and durations, may play a role in HRT’s effects on breast tissue. Evidence states that conjugated equine estrogen (CEE), compared to estro-progestin therapy, shows a better profile risk (HR 0.79, CI 0.65–0.97) and that, among different type of progestins, those structurally related to testosterone show a higher risk (RR 3.35, CI 1.07–10.4). Chronic unopposed endometrial exposure to estrogen increases the risk of endometrial hyperplasia and cancer, whereas the association with progestins, especially in continuous combined regimen, seems to reduce the risk (RR 0.71, CI 0.56–0.90). HRT was also associated with a protective effect on colon cancer risk (HR 0.61, CI 0.42–0.87). Data about ovarian and cervical cancer are still controversial.
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