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Finasteride for the prevention of prostate cancer

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A large clinical trial has previously shown that the drug Finasteride can reduce a man's chance of being diagnosed with prostate cancer. A recent study has shown that this benefit continued, well after men stopped taking the drug. But Finasteride is a controversial drug and the FDA do not recommend taking in the long term to prevent prostate cancer.

Finasteride (also known as Proscar and Propecia) is a medication that inhibits male hormones. Finasteride inhibits the activity of an enzyme called 5-alpha-reductase. By doing this, the drug inhibits the conversion of testosterone into dihydrotestosterone - a more potent form of testosterone. This reduces the effects of testosterone on the body. Finasteride is currently used as a treatment for prostate enlargement, also known as benign prostatic hyperplasia. It's also used to treat baldness in men and excessive hair growth in women.

The Prostate Cancer Prevention Trial

The Prostate Cancer Prevention Trial was launched in the mid-1990s. Its aim was to ask if long term use of Finasteride reduced the risk of getting prostate cancer. This was a large, placebo-controlled, double-blind randomised controlled trial. Men were randomly assigned to receive either Finaseride or a dummy tablet (placebo). They didn't know which one they were taking. The researchers analysed the data, before knowing who had which drug, to reduce any possible bias. This type of trial is considered a gold standard test of the effectiveness of a drug.

The Prostate Cancer Prevention Trial was led by Prof Ian Thompson from the University of Texas Health Science Center in the US. 18,882 men were recruited to the Prostate Cancer Prevention Trial, from between 1994 and 1997. The men were 55 years or over at the start of the study. Half of these men took Finasteride and the other half took a placebo pill. They had PSA tests and digital rectal exams each year. After 7 years, the researchers recorded the number of men who were diagnosed with prostate cancer. They also performed a biopsy on each of the men to make sure they hadn't missed any cases.

24.4% of the men who took the placebo were diagnosed with prostate cancer, compared to 18.4% of the men who had Finasteride. The conclusions of the Prostate Cancer Prevention Trial were that Finasteride could reduce the risk of being diagnosed with prostate cancer by approximately 25%.

 A new study has been published that follows-up these men after an average of 16 years. Finasteride was only taken for 7 years. The latest study asked whether the benefits from 7 years of taking this drug were maintained in the long term. They used US Medicare records to ask how many men were diagnosed over an average 16 years of follow-up. To do this, they established a link between the clinical trial data and Medicare claims data. The US Medicare system is different to Australia's. It is a health insurance system for Americans over 65 years who have worked and paid into the system through their tax. So not all the men enrolled in this trial would have been covered by the US Medicare. The researchers managed to find the appropriate data for 75% of the men involved in the original Prostate Cancer Prevention Trial.

The 16-year follow-up showed that the benefit from 7 years of Finasteride was maintained. The group who took Finasteride had an overall 21.1% decreased risk of being diagnosed with prostate cancer compared to the group who took the placebo.

The problems with taking Finasteride to prevent prostate cancer

Unfortunately, there are good reasons that taking Finasteride to prevent prostate cancer is not recommended.

Finasteride has side effects. With long-term use there is a risk of decreased libido, erection problems, male breast growth and depression. When Finasteride is taken to treat baldness, these side effects are mostly manageable. But during the Prostate Cancer Prevention Trial, five times more Finasteride was taken per day than is used for baldness.

To investigate the side effects caused by Finasteride treatment, men in the study were interviewed regularly during their 7 years of treatment. The researchers found that reduced volume of ejaculate, erection problems, loss of libido, and breast enlargement were more common in men taking Finasteride than those taking placebo. These are considerable side effects for only a 21.1% decreased risk in diagnosis. But the men who took Finasteride were less likely to suffer from urgency to urinate, prostate inflammation and urinary tract infection.

But there is another major issue with long term use of Finasteride to prevent prostate cancer. Tumours of Gleason grade 7 or above were more common in the men who took Finasteride. 6.4% of the men who took Finasteride had high-grade tumours compared to 5.1% of the men who took placebos. These results indicate that treatment with Finasteride may somehow be promoting the growth of higher-grade prostate cancers. This would certainly detract from any benefit of reduced risk of diagnosis.

The researchers reanalysed their data and predicted that the treatment had made the higher-grade tumours easier to find. They believe that a smaller prostate volume, making it easier to find tumours, and other factors, have led to a greater rate of high-grade prostate cancer diagnoses in those taking Finasteride.

These arguments have not been sufficient to convince the US Food and Drug Administration (FDA) that Finasteride would be a safe way to prevent prostate cancer. Most concerning, is that a similar effect on tumour grade was found using the drug Dutasteride (Avodart). This drug also inhibits 5-alpha-reductase enzymes, lowering the effects of testosterone. Dutasteride is used to treat prostate enlargement and hair loss. The 4-year REDUCE clinical trial asked if Dutasteride could also prevent prostate cancer. In this trial, men who took Dutasteride had a reduced rate of prostate cancer diagnoses. But similar to Finasteride, those who took Dutasteride had a higher chance of being diagnosed with a high-grade prostate cancer.

Due to the results of the REDUCE and Prostate Cancer Prevention Trials, the FDA have issued a warning that:  5-alpha reductase inhibitors may increase the risk of a more serious form of prostate cancer.

 

Currently we do not have drugs that are recommended to safely prevent prostate cancer. PCFA recommends evidence-based lifestyle choices to help prevent cancer, such as maintaining a healthy body weight, eating a healthy diet (such as a Mediterranean-style diet), regular exercise and minimising processed meat consumption.

 

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