The role of long-term MHT in the prevention and management of osteoporosis remains controversial, following results of the Women’s Health Initiative (WHI) study of combined oestrogen and progestin therapy4 and its study of oestrogen-alone therapy.2
Tibolone has a different side effect profile from traditional MHT. A Cochrane systematic review found no evidence for an increase in breast cancer in women with no history of breast cancer (OR 0.52; 95% CI: 0.21–1.25).9 However, tibolone does appear to increase breast cancer recurrence in those with treated breast cancer.9,10 There is no evidence for increased heart disease or thromboembolic events with tibolone, but in older women there was an increased risk of stroke.3
Raloxifene may increase hot flushes and is likely to aggravate vasomotor symptoms. Like traditional MHT, raloxifene is associated with increased thromboembolic events, but has not been associated with heart disease or overall risk of stroke.11 In one study of women at high heart disease risk, raloxifene increased fatal, but not overall, stroke risk.7
Evidence Statement
Treatment effect
In a clinical trial of 7705 women randomised to two doses of raloxifene or placebo followed for up to four years, there was a reduction in vertebral fractures (RR 0.64; 95% CI: 0.53–0.76) at the approved dose of 60 mg per day.8 There was no significant reduction in non-vertebral fractures (RR 0.93; 95% CI: 0.81–1.06). Similar results were found for another good-quality study of raloxifene in over 10,000 women at high risk of heart disease at baseline.7
There is good evidence that, compared with placebo, oestrogen is associated with a decreased risk of vertebral, non-vertebral, and hip fractures. This effect was observed in the analysis for all postmenopausal women (OR not reported), as well as for groups at higher risk of fractures (RR ~0.7).1 In two clinical trials conducted by the WHI, conjugated oestrogen in combination with progestin in postmenopausal women (n=16,608) or conjugated equine oestrogen (CEE) alone in women after hysterectomy (n=10,739) were shown to reduce the risk of osteoporotic fractures.2,4 Participants taking CEE 0.625 mg and medroxyprogesterone acetate 2.5 mg per day in a combined tablet (as opposed to oestrogen therapy) for an average of five years had significant reductions in total fractures (HR 0.76; 95% CI: 0.69–0.85; P=0.05) and hip fractures (HR 0.66; 95% CI: 0.45–0.98; P=0.05).4 Participants taking CEE 0.625 mg per day for an average of six years had significant reductions in the rates of all osteoporotic fractures (HR 0.70; 95% CI: 0.63–0.79; P=0.01) and hip fractures (HR 0.61; 95% CI: 0.41–0.91; P=0.01).3 An RCT of tibolone in 4500 women over three years found decreased risks of vertebral fracture (HR 0.55; 95% CI: 0.41–0.74) and non-vertebral fracture (HR 0.74; 95% CI: 0.58–0.93).3
Safety
Oestrogen alone or combined with progestagens
The WHI reported that in the oestrogen-alone group there was no increased risk of invasive breast cancer or cardiovascular disease, although the other outcomes were similar to the combined group.2 For the combined oestrogen/progesterone group, increased risk of invasive breast cancer has been reported in multiple analyses, although the initial report of increased coronary heart disease was no longer significant in subsequent analyses.2–5,9 Increased risks of thromboembolic events and stroke are reported for both groups. Subsequent to the initial publication, there have been multiple reanalyses of the data, including by age of initiation of MHT. The side effect profile is more favourable for those women starting MHT within 10 years of menopause (age 50–59 years) with low absolute risks of thromboembolic events and stroke.9
In a large meta-analysis12 and nested case-control study,13 the risk of breast cancer increased steadily with longer duration of MHT use and was greater in those on combined oestrogen/progesterone therapy compared with oestrogen alone, with the increased risk persisting for several years following cessation.12 Different progesterones are associated with differential breast cancer risk, with micronised progesterone having the lowest risk.14
Long-term follow-up (median follow-up >20 years) of the WHI study cohort found that CEE alone compared with placebo in women with hysterectomy was associated with lower breast cancer incidence (HR 0.78; 95% CI: 0.65–0.93) and lower breast cancer mortality (HR 0.60; 95% CI: 0.37–0.97).15 However, compared with placebo, CEE plus medroxyprogesterone acetate in women with a uterus was associated with higher breast cancer incidence (HR 1.28; 95% CI: 1.13–1.45), but no difference in breast cancer mortality (HR 1.35; 95% CI: 0.94–1.95).15
The most recent systematic review that looked at 27 RCTs and 47 observational studies between 2009 and 2019 reported an increased risk of thromboembolic events (for RCTs, summary estimate [SE] 1.70 [95% CI: 1.33–2.16]; for observational studies, SE 1.32 [95% CI: 1.13–1.54]).16 The authors noted that the study populations in the RCTs were older and had more underlying disease than those in the observational studies. In the same systematic review, an increased stroke risk was only seen in the RCTs (SE 1.14; 95% CI: 1.04–1.25) and a decreased risk of myocardial infarction was seen in observational studies (SE 0.79; 95% CI: 0.75–0.84).16 Multiple subgroup analyses were also performed to better understand the clinical effects of MHT. These analyses suggest that choice of MHT, underlying disease, and timing of initiation should be considered. In subgroup analyses of observational studies, a decreased risk of all-cause death was observed among oestrogen-only MHT (SE 0.85; 95% CI: 0.77–0.95) and early users after menopause (SE 0.68; 95% CI: 0.51–0.92).16 In addition, increased risk of stroke was seen in observational studies in women administered oral MHT (SE 1.24; 95% CI: 1.11–1.39), whereas a decreased risk of stroke was observed in women administered non-oral MHT (SE 0.86; 95% CI: 0.77–0.96). Overall, analyses favour earlier initiation (within 10 years of menopause) and non-oral MHT, and support safe use for at least five years in healthy women initiating treatment before the age of 60 years. The International Menopause Society supports tailoring MHT duration to the individual’s needs.17
Tibolone
An RCT of women aged >60 years reported a reduction in the risk of invasive breast cancer (absolute risk reduction [ARR] 1.9 per 1000 person-years; 95% CI: 0.5–3.4; P=0.02) and colon cancer (ARR 1.3 per 1000 person-years; 95% CI: 0.1–2.6; P=0.04) associated with tibolone therapy.3 However, the relative hazard for stroke was 2.19 (95% CI: 1.14–4.23) and the absolute risk increase was 2.3 per 1000 person-years (95% CI: 0.4–4.2), leading to early cessation of the trial. Absolute risk increased more in participants aged >70 years (absolute risk increase 3.1 per 1000 person-years). There was no increased risk of heart disease or venous thromboembolic events.3 In a subsequent study of women already treated for breast cancer, tibolone was found to decrease vasomotor symptoms and maintain BMD, but there was an increased risk of breast cancer recurrence (HR 1.40; 95% CI: 1.14–1.70).10 Similar to the earlier study, there was no increased risk of venous thromboembolic events or heart disease in this younger group.
Raloxifene
In the four-year follow-up of the pivotal raloxifene Multiple Outcomes of Raloxifene Evaluation (MORE) study,8,18 there was an increased risk of thromboembolic events, with an RR of 2.76 (95% CI: 1.30–5.86) for deep venous thrombosis and 2.76 (95% CI: 0.95–8.01) for pulmonary embolism. Unlike MHT, there was a reduced risk of breast cancer (RR 0.38; 95% CI: 0.24–0.58) and no increased risk of cardiovascular events.19 In a subsequent RCT of raloxifene in over 10,000 women with either established heart disease or risk factors for heart disease, there was a similar reduction in breast cancer (primarily estrogen receptor positive) and no increased risk of primary coronary events, overall risk of stroke or overall deaths.7 However, there was an increased risk of fatal strokes (HR 1.49; 95% CI: 1.00–2.24) and venous thromboembolism (HR 1.44; 95% CI: 1.06–1.95).7