The risks and benefits of HRT

The Women's Health Initiative (WHI) study, a large randomised trial comparing combination hormone replacement therapy (HRT) to placebo, found that the increase in risk associated with long term therapy exceeded the benefits.1 In particular the promise of cardiovascular benefit from HRT was unfulfilled and therapy was found to increase the risk of cardiovascular events (see Table below).

A further surprising result of the WHI study was an increase in the incidence of dementia with HRT using oestrogen plus progestogen, and a failure to enhance cognitive function.2 The WHI study did, however, demonstrate protection against fracture with oestrogen plus progestogen,1,3 but this protection, even in women with the highest risk of fracture in the study, did not outweigh the other negative effects.3

The Million Women Study (MWS), which had a prospective observational design, further emphasised the risks of HRT, indicating a higher risk of breast cancer with oestrogen plus progestogen than with oestrogen alone (see Table).4 The results indicated that the increase in the incidence of breast cancer with oestrogen plus progestogen (compared to oestrogen alone) was greater than the reduction in incidence of endometrial cancer associated with adding progestogen to oestrogen therapy.4 The MWS also reported a significant increase in the incidence of breast cancer with tibolone and with implanted and transdermal oestrogen-only preparations.

Following its comprehensive review of these studies and other available data, the Australian Drug Evaluation Committee has recommended:5

"The use of HRT for any long term disease prevention cannot be generally justified as the potential harm may out weigh potential benefits. This concern also applies to the use of HRT to prevent osteoporosis.

"HRT has an established place in the short term management of symptoms of the menopause. For treatment of established osteoporosis, the selection of HRT by the patient and doctor should be based on a careful consideration and discussion of risks and benefits for that individual."

In addition, ADRAC advises that HRT use be for as short a time as practical, and be reviewed regularly.

Reference

1. Writing Group for the Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women. Principal results from the Women's Health Initiative randomized controlled trial. JAMA 2002;288:321-33
2. Shumaker SA, Legault C, Rapp SR et al. Estrogen plus progestin and the incidence of dementia and mild cognitive impairment in postmenopausal women. The Women's Health Initiative Memory Study: a randomized controlled trial. JAMA 2003;289:2651-62
3. Cauley JA, Robbins J, Chen Z et al. Effects of estrogen plus progestin on risk of fracture and bone mineral density. The Women's Health Initiative randomized trial. JAMA 2003;290:1729-38
4. Million Women Study Collaborators. Breast cancer and hormone-replacement therapy in the Million Women Study. Lancet 2003;362:419-27
5. Australian Drug Evaluation Committee. Update to ADEC statement on use of hormone replacement therapy. 17 Oct 2003. http://www.health.gov.au/docs/html/hrtadec2.htm

Table: Changes in incidences of adverse events with HRT found in WHI Study and Million Women Study Adverse event Study Therapy Baseline rate (events per 10,000 women-years) Change in number of events per 10,000 women-years Cardiovascular disease           Coronary heart disease WHI O+P 30 7 extra1   Stroke WHI O+P 21 8 extra1   Venous thromboembolism WHI O+P 16 18 extra1 Cognitive function           Dementia WHI O+P 22 23 extra2 Fracture           All fractures WHI O+P 199 47 fewer3   Hip fracture WHI O+P 15 5 fewer1 Cancer           Breast WHI O+P 30 8 extra1   MWS O+P 21 12 extra4   MWS O 21 3 extra4   Endometrial MWS O   8 extra (estimate)4   Colorectal WHI O+P 16 6 fewer1

Abbreviations: WHI, Women's Health Initiative Study; MWS, Million Women Study; O, oestrogen; P, progestogen.
Note: These event rates are age-dependent: mean age in WHI 63 years; mean age at recruitment for MWS 56 years