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Can you prevent prostate cancer with a pill?

If you consider the men in your life who are older than 55 (and even those who are younger), it's a pretty good bet that balding, peeing often and fear of prostate cancer is on their radar.

There is a drug called finasteride (known by the brand names of Proscar and Propecia) that works somewhat for all of these issues.

Last week, the American Society of Clinical Oncology and the American Urological Association came out with a joint statement saying that family doctors such as me should discuss the pros and cons of taking finasteride and similar drugs, called 5-ARIs, to help prevent prostate cancer.

Finasteride started as a medication for benign prostate hyperplasia (BPH), an incredibly common condition that plagues 50 per cent of men aged 50 and 80 per cent of men aged 80.

Imagine your bladder as a water balloon that is constantly being filled each time you take a drink. There is a tube (your urethra) running off the bottom to drain it. In men, the tube runs through a small plum-sized gland (the prostate).

As men age, the prostate grows and constricts the drain tube. This means the water balloon fills up more quickly, sometimes to overflow, and men have to go to the washroom more often. Finasteride and other 5-ARIs shrink the prostate. This takes time, and other drugs such as alpha blockers that relax the prostate are typically used first.

Like many eureka moments in science, the early trials of finasteride showed something unexpected. The men started to get a little shaggy. Baldness was stalled or slightly reversed.

The cancer story started in October, 1993, at 221 sites across the United States with the Prostate Cancer Prevention Trial (PCPT). The trial was designed to determine whether finasteride could prevent prostate cancer in men older than 55. It was funded by the U.S. National Cancer Institute and cost $73-million (U.S.).

The men in the trial had low prostate specific antigen (PSA), a marker for prostate cancer, to begin with. Fifteen per cent had a brother, father or son who had prostate cancer.

The PCPT was expected to continue until May, 2004, but was stopped in June, 2003, when an analysis showed that finasteride reduced the relative risk of developing prostate cancer by 25 per cent regardless of race or family history.

So why haven't you heard about this? Well, the main reason was that enthusiasm was tempered by an increased rate of high-grade tumours, which are more likely to spread, in men taking finasteride. What has changed is that through reanalysis of the study and the research done since, most experts feel that, although further monitoring is necessary, the finding of high-grade tumours was likely a chance happening.

So how effective is finasteride in reducing the risk of prostate cancer and what are the downsides? Taking a pill for an illness is one thing. Taking one when you are well is another. Put another way, it would need to be pretty darn effective with minimal side effects to get me to sign up.

First, a little context. If you are a man older than 50 and you look around at your peers, you may notice that prostate cancer is common. One in six men will get it in their lifetimes. However, if 100 men get prostate cancer, 98 will be alive five years later. Most, but not all, prostate cancers are slow-growing and not necessarily life-threatening.

I said earlier that the relative risk of prostate cancer was reduced by 25 per cent for men who took finasteride. This is a good example of why you should always ask for the absolute risk because the relative risk can be misleading. The absolute risk reduction was 1.4 per cent, which isn't nearly as sexy or reassuring. If 1,000 men older than 50 were followed over seven years, 59 would be expected to develop prostate cancer. If they all took the drug, 45 would still develop cancer. Put another way, 71 men would have to take the drug for seven years to prevent one cancer.

Finasteride was well-tolerated, but there were some unpleasant side effects that included decreased sex drive and erectile dysfunction (11 to 40 men experience the side effect out of every 1,000 who take finasteride) and enlarged male breasts (20 to 30 men for each 1,000). Decreased cash flow is another side effect - finasteride can cost $60 a month. Finally, the recommendation calls for annual PSA testing, which can produce false positives and lead to unnecessary additional tests and treatments.

So what would I tell a patient? If I had bad BPH, was peeing all the time and wanted to add finasteride to my treatment, then prostate cancer prevention would be another really good reason to take it.

On the baldness issue, I personally side with Kris Kristofferson on this: "Freedom's just another word for nothing left to lose." But for patients who elect to stave off the inevitable, it is important to keep in mind that Propecia, sold for treating baldness, contains one milligram of finasteride, instead of the 5 milligrams found in Proscar used for BPH. The lower dose may not work for preventing prostate cancer.

As far as the average healthy male, there may be some of you who are quite fearful of prostate cancer and taking a daily pill seems reasonable. To me, taking a pill for seven years for a one in 71 chance that it will prevent prostate cancer seems a stretch.

Dr. Mike Evans is a family physician, associate professor and director of the Health Media & Innovation Lab at the Li Ka Shing Knowledge Institute of St. Michael's Hospital and the University of Toronto.

mevans@globeandmail.com