Compared to placebo treatment, taking 5-alpha-reductase inhibitors (5-ARIs) can reduce a man's risk of being diagnosed with prostate cancer from around 5-9% to around 4-6% during up to 7 years of treatment, according to a new Cochrane Review. However, those who are diagnosed with prostate cancer may be at a slightly increased risk of having a more dangerous (high grade) tumour. Additionally, the vast majority of cancers detected in these studies were very small and unlikely to cause any clinical problems during a man's lifetime.
Prostate cancer affects around 220,000 men each year in the USA alone, killing about 27,000 of them. Men over the age of 65 are at greatest risk. Safe and effective methods to prevent prostate cancer would be beneficial.
The hormone testosterone is one of the factors that may encourage these tumours to grow. There is now a range of 5-alpha-reductase inhibitors that disrupt the biochemical pathway that generates testosterone, therefore potentially reducing the incidence of prostate cancer development.
A group of Cochrane Researchers searched existing literature for trials that looked at the effects of these drugs in men. They found good and bad results.
On the positive side, the drugs led to slight decreases in the incidence of prostate cancer and can improve common benign lower urinary tract symptoms such as hesitancy, straining, frequency and night time urination.
On the negative side, when cancer was detected it was more likely to be of a high grade in men receiving 5 alpha reductase inhibitors. The reason for this is uncertain, and could be because the drugs alter the way that the tumour cells grow. However, it could be that these drugs just alter the way the cells look under the microscope rather than affecting their clinical prognosis. In addition there was evidence with one 5-ARI (finasteride) that it has a tendency to impair sexual or erectile function.
"There is a lot we still don't know and future research must determine whether 5-ARIs reduce the overall risk of dying from prostate cancer, whether any of the different 5-ARIs on the market does a better job than the others and whether the potential benefits outweigh the risks," says lead researcher Dr Timothy Wilt, Coordinating Editor of the Cochrane Prostatic Disease and Urologic Cancers group based at Veterans Affairs Medical Centre in Minneapolis, Minnesota, USA.