Screening for Prostate Cancer – Again

I’ve already reviewed this topic in an earlier post, but it keeps coming back. The Aug 5, 2008 issue of the Annals of Internal Medicine contains two papers dealing with this issue. The first presents Screening for Prostate cancer: US Preventative Services Task Force Recommendation. It concludes what has been obvious to those not carried away by reckless enthusiasm – “Current evidence is insufficient to asses the benefits and harms of screening for prostate cancer in men younger than 75 years.” It goes on to state with directness unusual in the Annals of Internal Medicine: “Do not screen for prostate cancer in men age 75 or older.”

The second paper Benefits and Harms of Prostate-Specific Antigen Screening for Prostate Cancer: An Evidence Update for the US Preventative Service Task Force concludes that “PSA screening is associated with psychological harms and its potential benefits remain uncertain.”

These conclusions seem counter intuitive especially after all the propaganda emanating from the American Urological Association and the American Cancer Society which vigorously recommend PSA screening in almost anyone. Actually the same people write the advisories for both groups. The current Task Force recommendations will almost certainly have no effect on AUA’s or the ACS’s positions on PSA screening. The problems with screening are many fold. First about 90% of prostate cancers are so mild that the patient will likely die from something else before his prostate cancer gets him. In these patients you get all the side effects of diagnosing and treating a disease without any benefit. These patients are said to die with prostate cancer not from it.

The side effects of treating prostate cancer are formidable. Depending on the modality employed they include impotence, incontinence, and radiation-induced bowel injury. These are complications that one would tolerate only if sure of a benefit. The incidence of these complications is 25 to 50%. The remaining 10% of prostate cancers are the ones that may prove lethal and are thus the group that might benefit from screening. Let’s assume that early treatment (this is only an assumption not a fact) saves one out of these 10 patients that have a lethal form of the disease. This is a 10% reduction in prostate cancer mortality, an impressive achievement. But you have to treat 100 patients to save one. Fine if you’re the one saved, not so good if you’re one of the 99 that gets no benefit from the treatment and is at high risk for the side effects described above.

Screening for prostate cancer, under the assumptions above, has a 1% chance of benefit versus a 25 to 50% chance of harm if the screening reveals the disease. But since many patients with elevated PSAs do not have cancer, many patients will under go prostate biopsies that show benign disease. Thus we might have do 200 biopsies (probably more) to find 100 patients with prostate cancer which will find one patient who benefits from all this frenetic diagnostic activity. This is why routine PSA screening makes little sense.

The problem would be greatly simplified if we could tell in advance which are the prostate cancers that are potentially lethal and which are not. If we could do this the risk/benefit ratio would be much more favorable; but alas we lack the knowledge to make accurate predictions. And on top of this we still don’t know whether treatment of the disease applied early is any better than that offered after the disease has declared itself.

Sadly, most doctors are not up to speed on this issue. Before you consent to PSA screening have a discussion about its value with your doctor. If he hasn’t read the papers cited above ask him to. PSA screening, as is true for most medical screening, should be an individual decision based on sober consideration of the data for and against its use.

Finally, the strong recommendation against screening men 75 and older should be obvious as you’ve gotten this far. These patients have a reduced life expectancy by virtue of their advanced years. There’s little reason to screen for a disease that takes many years to kill people especially if such screening is of unproven value in any age group.

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