Does hormone replacement therapy cause breast cancer

Based principally on findings in three studies, the collaborative reanalysis (CR), the Women’s Health Initiative (WHI) and the Million Women Study (MWS), it is claimed that hormone replacement therapy (HRT) with estrogen plus progestogen (E+P) is now an established cause of breast cancer; the CR and MWS investigators claim that unopposed estrogen therapy (ET) also increases the risk, but to a lesser degree than does E+P.

Publication of the Million Women study in 2003 raised concerns about risks of HRT, in particular increased risk of breast cancer. This concerning news followed closely in the wake of the WHI trial, first published in 2002, which also emphasised risks of HRT. Not surprisingly, there followed a sudden loss of confidence in the use of HRT and a decline in prescriptions. Subsequently, attempts have been made to make sense of the study results. The most recent report from the Journal of Family Planning and Reproductive Healthcare, available now online, has examined in detail the data used in the Million Women study (MWS) and concludes that the evidence in the MWS was unreliable and that HRT may or may not increase the risk of breast cancer, but the MWS did not establish that it does.

With reanalysis of the WHI trial also now showing that, when used appropriately, and especially in women under the age of 60 HRT is safe, surely the time has come for women and healthcare professionals to worry less about risks of HRT and return to considering the benefits and see HRT as a very useful option for women experiencing menopausal symptoms, or suffering from osteoporosis or premature ovarian failure.

What are the risks of HRT?

Although HRT can offer many benefits, for some women it can carry unacceptable potential risks. When deciding whether or not HRT is right for you, you must consider the balance between risks and benefits.

The main potential risks that have been identified are:

• breast cancer

• blood clots in the veins (venous thrombosis)

• blood clots in the arteries (heart attacks and strokes)

• cancer of the lining of the uterus (endometrium), though this can be prevented by the addition of progestogen.

It is important to understand these risks and put them into perspective – most women taking HRT do not experience any of these problems as a direct result of taking the hormones. Furthermore, other risk factors are often more important than HRT – particularly smoking or being very overweight – in creating these problems.

Evidence suggests that women with a family history of breast cancer have the same relative increase in risk of breast cancer from hormone replacement therapy (HRT) as the general population. Limited evidence suggests HRT does not increase the risk of breast cancer in women who carry the BRCA1 mutation.