br Menopausal hormone therapy from
Menopausal hormone therapy, from the beginning to WHI Estrogen products have been used since the 1940s, with increasing prescription through the 1960s. First concerns appeared in the 1970s when oral treatment was linked to uterine cancer. Oral estrogens have traditionally been coupled with progestogen to protect against endometrial hyperplasia, which can lead to endometrial cancer, unless the woman is hysterectomized (de Villiers et al., 2013; NAMS, 2012). Progestogens include both progesterone, produced from cholesterol in the ovaries and in the adrenal glands, and synthetic progestins derived from progesterone (pregnanes and 19-norpregnanes) or from testosterone (19-nortestosterones). MHT was initially prescribed for short-term treatment of postmenopausal symptoms and observational studies suggested that this treatment was associated with prevention of Afatinib dimaleate mass disease, osteoporosis and Alzheimer\'s disease (Canderelli, Leccesse, Miller, and Unruh Davidson, 2007; Mauvais-Jarvis, Clegg, and Hevener, 2013). Long-term MHT was then proposed with this expectation of such associated benefits. Due to the large increased number of prescriptions of MHT, the National Institutes of Health started the Women\'s Health Initiative (WHI) study to examine the potential risks and benefits associated with such menopausal treatment. In 2002, the initial results of this randomized trial, including approximately 16,000 postmenopausal women, were published after a mean of 5.2 years of treatment with conjugated estrogens (CE, which is a mixture of estrogens extracted from the urine of pregnant mares) in combination with synthetic progestin: medroxyprogesterone acetate (MPA). The message to the public and physicians was that this hormonal combination was associated with an increased incidence of thrombotic events, coronary diseases and breast cancers (Rossouw et al., 2002; Scarabin, 2014a). The second arm of the study included hysterectomized postmenopausal women receiving either CE alone or placebo. This second trial, after a follow up of almost 7 years, showed no worsening of coronary risk and no increased risk of breast cancers (Anderson et al., 2004). However, a trend towards increased risk of venous thromboembolism (VTE) and a significant increase in risk of stroke was observed in hysterectomized women treated with CE alone (Anderson et al., 2004). Prescriptions of MHT rapidly dropped following the dissemination of these negative messages to the public by the media, despite the major limitations of the WHI study regarding, in particular, the age of the participants, being very significantly distant from the menopausal age. This outcome resulted from the major impact of age on cardiovascular events, whose incidence dramatically increases with time. Indeed, almost a quarter of the women in the WHI study were over 70 years and the combination of estrogen with progestogen was detrimental in terms of coronary events essentially in this subgroup of aged women, whereas younger women on MHT had similar coronary events as those on placebo, leading to the “timing” hypothesis (Lenfant et al., 2011; Arnal et al., 2017; Rossouw et al., 2007; Valera, Gourdy, Tremollieres, and Arnal, 2015). In contrast, it appears that younger women (<60 years) have a more favorable risk–benefit profile when using MHT compared to older women (de Villiers et al., 2016; Lobo, 2017). Moreover, MHT may be used with minimal risk in the first 5 years following the onset of menopause. In addition, the type of progestogen has recently emerged as an important determinant of the VTE risk among MHT in a meta-analysis based on observational studies (Kuhl, 2005; Scarabin, 2014b). There is a striking contrast between American and European practices regarding the type of progestogens used. In the USA, medroxyprogesterone acetate (MPA) is used almost exclusively, while a wide variety of progestogens are prescribed in European countries, where progesterone is the most commonly used (Canonico et al., 2007; Scarabin, 2014b; Stanczyk, Hapgood, Winer, and Mishell Jr., 2014). Finally, the impact of the route of estrogen administration on thromboembolic events has been investigated (Scarabin et al., 2003), showing an increased risk of venous thromboembolism in users of oral postmenopausal estrogen, but not of transdermal estradiol (E2). This increased VTE risk appears to be attributable to the hepatic first-pass, since it is associated with an increase of circulating blood coagulation factors only observed when the oral route is involved (Olie et al., 2011). Estrogen and progestin combination also increased the risk of breast cancer in the WHI trial, whereas hysterectomized women treated with CE alone (without progestin) developed even fewer breast cancers than women receiving placebo (Anderson et al., 2004; Rossouw et al., 2002). The identification of safer estrogenic compounds for MHT is thus needed.