Prostate cancer:The problem with the PSA test

The prostate is a walnut-sized organ that sits invisibly between the rectum and scrotum, close up against the bladder. It surrounds the urethra, the tube which carries urine. Its only function appears to be to provide liquid to transport sperm on their journey from testes to cervix.

Problems with the prostate occur out of all proportion to its biological importance. Up to age 30, it’s normally trouble-free but, from 30 to 50, it can become inflamed due to a bacterial infection (prostatitis). Later in life, it may become enlarged. This growth may be cancerous, but if it’s non-cancerous, it’s called benign prostatic hyperplasia (BPH).

Because the prostate surrounds the urethra, trouble with urination is usually the first sign of a problem. Symptoms include weak or intermittent urine flow, incomplete voiding, frequent or painful urination and incontinence. The difficulty with self-diagnosis is that all three prostate conditions may produce any of these symptoms.

Prostatitis is the easiest to diagnose. Because it’s caused by a bacterial infection, a simple urine culture test will often spot it.

BPH – a benign enlargement of the prostate – is more difficult to diagnose when trying to decide between it and cancer. The most elementary test is to feel for an enlarged prostate.

If indeed an enlargement is found, the next stage of diagnosis is more complex, problematical and controversial.

Twenty years ago, prostate experts thought they had found the answer when a protein was found in men’s blood that seemed to correlate with the presence of prostate cancer. Although it was quickly named ‘prostate-specific antigen’, there was soon some doubt as to how ‘specific’ the PSA test actually was.

The first major problem was that the test cannot reliably distinguish between cancerous and non-cancerous prostate enlargement. It also throws up many false positives and false negatives, so that cancers are either missed or men are subjected to unnecessary treatment (Urologe A, 2000; 39: 22-6). As one report baldly puts it: ‘. . . two-thirds of men with an elevated PSA level do not have prostate cancer’ (Semin Urol Oncol, 1996; 14: 134-8). Finally, there is considerable disagreement over what PSA levels are clinically relevant.

Despite these problems, there has been pressure to use PSA as a screening test in much the same way as mammography was once championed for breast cancer. Enthusiasts claim increased accuracy from new techniques that measure PSA density or relate the test to the patient’s age, but the results are still not clear-cut (Urol Clin North Am, 1997; 24: 323-32).

Many experts now admit to ‘a lack of credible evidence’ that PSA screening saves lives. Worse still, they say that screening has actually harmed and even killed people due to the unnecessary treatment it leads to. A recent Yale University report concluded that screening and the subsequent treatment based on often faulty diagnosis ‘can be associated with considerable morbidity and mortality in the context of a disease that is often not fatal’ (J Sci Am, 2000; 6 [Suppl 2]: S188-92).

One diagnostic test often given by doctors after a positive PSA reading is a biopsy. This involves taking ‘tissue cores’ from as many as 12 places on the prostate to look for cancer cells. The procedure is not without risk: most patients become infected from the procedure itself, 20 per cent suffer severe pain and 15 per cent are rendered impotent (J Urol, 2001; 165: 445-54). There’s also evidence that biopsies themselves may be inaccurate, often failing to detect cancerous tissue (Prostate Cancer Prostatic Dis, 2000; 3: 13-20).

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Written by What Doctors Don't Tell You

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