HRT and breast cancer: here is what you should know

    23 August 2016

    A large new study has found that the most common form of hormone replacement therapy (combined HRT) nearly triples the risk of breast cancer. This is perhaps a higher risk than was previously thought. It is incredibly useful, serving to give patients more information than they had before.

    However, estimates of risk are useless without context. So here is the background.

    Ever since the publication of the Women’s Health Initiative and Million Women Study, attention has been rightly paid to the potential risks of HRT, particularly regarding the risk of breast cancer in women. Before these publications, many were touting HRT as the panacea of all menopausal ills, relatively free of side effects and risks.

    These studies suggested that in women taking ‘oestrogen-only’ HRT, the risk of breast cancer was not increased and indeed there appeared to be a slight protective effect. This kind of HRT is given to women who do not have uteruses.

    In contrast, combined or ‘estrogen-progestogen’ HRT was found to increase the risk of breast cancer by a magnitude of eight additional cases per 10,000 women a year.

    Subsequent studies have affirmed this relationship, with several noting a decrease in breast cancer cases following the widespread decline in patients taking HRT. (Though other studies have found no such relation.)

    The latest study suggests that the risk of breast cancer remains elevated after both five and 15 years of combined HRT use. That is, the risk is roughly tripled. However, risk is unchanged with the use of oestrogen-only HRT.

    Should women be worried by this? The risks must be put into perspective. According to Cancer UK, only three per cent of breast cancer cases in the UK are related to use of HRT. Meanwhile, nine per cent of breast cancer cases are linked to obesity, six per cent to excessive alcohol consumption and three per cent to physical inactivity. Funnily enough, while all are modifiable risk factors, media attention focuses on HRT and ignores the rest.

    HRT has undoubted benefits, which include improved mood, sleep, abolition of troublesome night-sweats, a decrease in colon cancer risk for combined HRT, prevention of vulvovaginal atrophy (that is, the thinning, drying and inflammation of the vaginal walls) and thus painful sexual intercourse and repeated urinary tract infection, as well as reduced osteoporosis and fractures; started in healthy women within 10 years of menopause, oestrogen-only HRT has been shown to reduce cases of ischaemic heart disease.

    There are other potential side effects, however, which differ depending on the kind of HRT being administered. You can click on the tables below to view these.

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    The study that established these risk margins was performed, in most cases, one could argue, on a high-risk population for whom HRT should not have been started. Thus HRT was essentially the straw that broke the camel’s back.

    Ultimately, risk must be put into context. For some women, the trade-off between benefits of HRT versus breast cancer risk can be made within a framework of improved attention to overall health; risk can be mitigated considerably if you lose excess weight, reduce alcohol consumption and do more physical activity.

    For others, of course, the risk will be considered too high. Ultimately, though, there are many forms of HRT. Local forms (creams or vaginal tabs) as opposed to systemic (pills and patches) have never demonstrated complications in terms of cancer. These allow clinicians considerable flexibility in addressing the health needs of women and the risks involved.