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Studies Cast New Doubt on Prostate Cancer Screening

March 19, 2009 at 6:35 PM EDT
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Recent studies show that screenings for prostate cancer may not reduce death rates and may also lead to unnecessary treatment. A medical researcher discusses the latest findings.

RAY SUAREZ: Millions of men take a blood test annually to see if they have any indications of prostate cancer, but there have been growing questions about the value of the PSA test, as it’s known.

A pair of studies in the New England Journal of Medicine are adding more fuel to the controversy surrounding screening. Researchers in the U.S. and Europe independently followed a total of more than 250,000 men over a period of years. They found separately that the PSA test did not significantly reduce death rates.

The European study also suggested that, in many cases, the blood tests may have led to unnecessary treatment.

To help us understand more about the findings and questions, we’re joined by Andrew Vickers. He specializes in prostate cancer research as a statistician at Memorial Sloan-Kettering Cancer Center in New York.

And, Andrew Vickers, you had a large number of test suggests. You were able to follow them — or the researchers were — able to follow them for a long time in a large number of countries. So what were they trying to answer? And what did they find out?

ANDREW VICKERS, Memorial Sloan-Kettering Cancer Center: Well, there are two very different studies going on. There’s the one, as you mentioned, in the U.S. and the one in Europe. And they’re really quite different studies.

The U.S. situation is really quite different, because a lot of men are out there and they’re having PSA tests. And this was pretty much irrespective of what the researchers asked them to do. In the U.S. study, about half of the patients entering the study had already had a PSA test. And even those who were assigned to the control group, about a half of those continued to have PSA tests during the study.

In Europe, it’s really a very different situation. PSA testing hasn’t become part of routine medical practice, and very few men have had a PSA test entering the trial and only a small proportion of those in the control group actually went ahead and had a PSA test during the trial.

So they’re really quite different trials, and I think that’s reflected in their different results. The U.S. results didn’t find an important difference between the men told to have PSA tests and the men who were recommended to avoid the PSA tests.

In Europe, you did see a small, but statistically significant drop in mortality — about a 20 percent reduction in death from prostate cancer — in men advised to undergo the PSA test.

The method behind the exam

RAY SUAREZ: What is a PSA test? And does a higher number reliably reflect the presence or a lower number reflect the absence of cancer?

ANDREW VICKERS: OK, so PSA stands for prostate specific antigen. Antigen is a protein, and it's specific to the prostate, because you only find that protein in the prostate.

So what a doctor does is take a blood sample. And if he or she finds some PSA, some prostate specific antigen in your blood, that's a sign that there's something wrong with your prostate. The prostate should not be leaking chemicals such as the prostate specific antigen into your bloodstream.

The point about the prostate specific antigen is it's specific to the prostate; it's not specific to prostate cancer. All it tells you is you have some kind of problem in your prostate, and that might be due to cancer, but it might also be due to other causes, such as an infection or to benign changes within the prostate.

Generally speaking, men with a higher PSA value -- and we're talking typical values might be, say, four, five, or six -- are at increased risk of cancer.

But even if your doctor tells you, you have -- your PSA test has come back positive, you're still at lower than 50-50 chance of actually having prostate cancer. Most men with an elevated PSA actually do not have prostate cancer.

Potential to save lives

RAY SUAREZ: Well, more screening and more testing resulted in more treatment. Did more treatment end up with more men living longer and healthier lives?

ANDREW VICKERS: You did see that in the European study. You saw about a 20 percent reduction in death from prostate cancer.

What the European research has pointed out, though, was that a very large number of men had to be treated in order to prevent one death from prostate cancer. It was about, roughly speaking, a 50-1 ratio.

And that's clearly a problem with screening, is you are detecting a lot of prostate cancers that would never impact a man during his life. And, in fact, we've done studies at our own institution examining the prostates of men who've already died of other causes.

And in a 70-year-old man, for example, there's about a 40 percent chance of having detectable prostate cancer on autopsy. And this is obviously, because the man died of other causes, a prostate cancer that would never have affected him and did not affect him during his lifetime.

RAY SUAREZ: So, briefly, is there a simple answer to the question, does prostate cancer screening save lives?

ANDREW VICKERS: I wish there was a simple answer to that question. I think one thing to bear in mind is we do these very large studies. And when it ends, we think, "Right, that's it, the study's ended, we have our answer." And science, really, is a little bit more complicated than that.

I think we need some time to digest the data, try and understand what it means. These studies will continue. We'll continue to follow these men. We'll continue to analyze data from these studies. And then we'll try and understand what that means and make appropriate guidelines for the U.S. public.

What I will say is that what -- the studies were designed way back in the early '90s. And they really did reflect state-of-the-art in the early '90s.

But since that time, we've learned a lot about prostate cancer. And the couple things that we've learned are really very pertinent to the issue of prostate cancer screening.

The problem with prostate cancer screening is that we're detecting too many cancers that won't affect somebody's life, and maybe we're not treating those cancers as well as we might.

What we've learned about prostate cancer in the meantime is how to treat it better and also how to tell who has an aggressive prostate cancer that really needs to be treated and who has a less aggressive prostate cancer that might be treated by what's called active surveillance.

So we're not actually going in and removing the prostate or treating it with radiation. We're just following a man over time, just to make sure that that cancer doesn't become aggressive. So I think our increased knowledge of prostate cancer...

RAY SUAREZ: I'm going to have to stop it there, Andrew Vickers, but thanks a lot for helping us out in New York.

ANDREW VICKERS: Thank you very much.