Women’s HRT patches can treat prostate cancer just as effectively as standard hormone injections – but with fewer of the worst side-effects – according to a large UK trial published in the New England Journal of Medicine. The finding could change how men with prostate cancer that has spread beyond the gland are treated for years to come.

Standard treatment has long relied on shutting down testosterone, the fuel that drives many tumours, through regular injections that turn off the body’s own hormone production. They are effective, but they are blunt tools, dragging down oestrogen as well as testosterone and taking a heavy toll on quality of life with hot flushes, brittle bones and metabolic problems. Now, in an elegant twist of biology, the very hormone patches used to ease menopause symptoms in women are being repurposed to treat prostate cancer in men.

The idea sounds counterintuitive at first. Why would giving oestrogen to men help control a cancer fed by testosterone? The answer lies in feedback loops.

Oestradiol, the form of oestrogen in standard HRT patches, signals to the brain that there is plenty of sex hormone around. The brain then dials down its instructions to the testes to make testosterone, so levels of the male hormone fall just as effectively as with injections designed to switch production off directly. In other words, you can arrive at the same hormonal destination by a more subtle route.

In the new trial, more than 1,300 men, with an average age of about 72, were randomly allocated to either the standard hormone injections or to skin patches delivering oestradiol, identical to those used for menopausal........

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