Finasteride, also known as Proscar, is a medicine that has been around awhile. We give it to older men to shrink large prostates that are causing problems passing their urine, although nowadays we usually use one of the Alphablocker medicines to relieve symptoms first, and only use Proscar if they faint or get dizzy on these pills.

Finasteride in smaller doses is also called Propecia,  a pill taken to treat baldness.

Well this medicine is now being examined by scientists to see if it can prevent prostate cancer. Preliminary studies suggest that it could prevent 30% of prostate cancer, which comes to about 100thousand cases a year.

But before you run out and buy some, you might want to look at the facts.

Prostate cancer is common, but many cases just grow so slowly that you don’t know you have it. It is a common finding on autopsy of men dying of other causes.

But it is also a major killer of men, and some cases are in younger men.

The problem: So far there is no easy way to tell the slow growing type from the lethal type. And to make things worse, the most lethal types may kill you no matter what you do.

Doctors were happy when they developed the PSA test, which let us diagnose early cases. Except that sometimes a PSA would be high from other reasons (prostate infection is one cause). That causes a lot of worry until you treat and repeat the test.

But the real problem is if you find a mildly high PSA test. That means a referral, and possible needle biopsy.Ouch.

And then, what do you do if you find prostate cancer? Do you do the whole shebang and treat the guy, maybe leaving him impotent and leaking for the rest of his life, when maybe he will either die anyway, or maybe he has one of the slow growing cancers that wouldn’t kill him anyway, and you’ve caused him a lot of pain, and cost a lot of money, for something that didn’t need to be treated.

Not an easy choice.

Needless to say, unless you are at death’s door, we treat.

Well, anyway, the new test made the rate of prostate cancer go up high, not because there were more cases, but because we found a lot more early cases. That’s what thetable on the right shows: lots more cases being diagnosed, but only a small decrease in the number of men dying of prostate cancer.

But what happens if you give men Finasteride, which is known to shrink prostate tissue? The bar graft shows that the cancer rate is much lower taking Finasteride

Now, look at the graft on the left again. It shows that a lot of the cases are the “not lethal” types of prostate cancer, and so taking Finasteride doesn’t decrease the rate of dying as dramatically as  the 30% quoted in the NYTimes story. But it does decrease it some, and that is important news.

For years, we’ve known that our men using Proscar for large prostate glands would have their PSA blood test go down. But early studies of men taking Proscar for large prostate glands suggested that  it might stop the “non lethal” types of cancer, making the more lethal ones more common.

Now studies suggest that it not only lowers the cancer rate, but it also lowers the rate of the bad, fast growing prostate cancers. Very good news.

But without more long term studies it won’t be known if it indeed actually prevents the disease.

So what should you do?

Well, doctors are still debating whether or not to screen everyone with a PSA test, let alone treat men.

However, like most medicines, Proscar does have allergic side effects, and a small number of men will become impotent on it. (8% vs 3.5 % on placebo). If you have a large prostate that is making it hard to pass urine, and other medicines for large prostates don’t work or you can’t take them, rather than surgery for a benign disease,  I’d take the Proscar.

But to take it for 20 years to maybe stop a cancer? I’d wait for more information before I’d do that.

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Nancy Reyes is a retired physician living in the rural Philippines. Her website is Finest Kind Clinic and Fishmarket, and she writes medical essays at Hey doc xanga blog.

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