Dutasteride, a drug already used to treat men with enlarged prostates, can also slow the growth of early-stage prostate cancer that hasn't spread, according to research from Canada.

Published in the Lancet, the research suggested that giving dutasteride to men with early-stage disease could reduce or delay the need for radiotherapy or surgery, treatments that can sometimes cause impotence and incontinence.

This new study, led by Dr Neil Fleshner, from Princess Margaret Hospital in Toronto, looked at 302 men aged 48 to 82 years with low-risk prostate cancer that had not spread.

The men were given either dutasteride or a placebo once a day for three years. They also had biopsies after 18 months, and again after three years, to measure whether their disease had progressed.

The results showed that 38 per cent of the men receiving dutasteride saw their disease get worse, compared with 48 per cent given the placebo.

On top of this, men treated with dutasteride reported lower cancer-related anxiety throughout the study compared with those given placebo, possibly as a result of having lower PSA levels.

Dutasteride is already approved for the treatment of non-cancerous enlargement of the prostate. It works by blocking the conversion of testosterone to the male sex hormone dihydrotestosterone - which is involved in the development of prostate cancer - and has been shown to reduce the volume of some prostate cancers.

However, other studies have suggested that dutasteride and related drugs can encourage the growth of more aggressive, high-grade prostate cancers, and experts cautioned that more work was needed to fully understand the balance between risks and benefits.

Prostate cancer is the most common cancer in men in the UK - over 37,000 men are diagnosed with the disease each year. But many men have the low-risk form of the disease, for which so-called active surveillance can be appropriate. This involves having regular assessment and biopsies to keep track of the cancer instead of having treatment immediately.

In an accompanying editorial, Professor Chris Parker from the Royal Marsden in Sutton cautioned: "These data are consistent with the hypothesis that dutasteride reduces the volume of low-grade prostate cancers but has no effect, or even an adverse effect, on the progression of high-grade disease. Thus, although reducing overall prostate cancer detection, dutasteride could plausibly have no effect (or possibly a deleterious one) on prostate cancer mortality."

Liz Woolf, head of Cancer Research UK's patient information website, CancerHelp UK, echoed these concerns: "Men with 'low-risk' prostate cancer can face considerable uncertainty, and often have to decide whether to be regularly monitored or opt for immediate treatment, such as radiotherapy or surgery. So a treatment that may enable them to avoid or delay more invasive treatment could be useful.

"But as with all treatments, men would need to be fully informed of the likely benefits compared to any side effects it may cause. We need to see more data on the nature of these risks before dutasteride could be recommended as a routine treatment for men with low-risk disease."

Source: CRUK