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PSA screening revisited

BOSTON, MASSACHUSETTS. Dr. Michael Barry of the Harvard Medical School and the Massachusetts General Hospital provides an excellent review of the current status of PSA screening for prostate cancer. Dr. Barry starts out by posing the question "Should a 65-year-old man with no risk factors for prostate cancer except his age and with a normal digital rectal examination undergo a PSA (prostate-specific-antigen) test?" Dr. Barry points out that whether or not to have a PSA test is controversial because of the following:

  • No randomized clinical trials have ever demonstrated that early detection and aggressive treatment of prostate cancer reduce mortality;
  • The treatments usually mobilized after a positive PSA test and biopsy (radical prostatectomy, radiation therapy or castration) are associated with severe side effects including impotence and incontinence.

He also emphasizes that the PSA test is not that accurate. A recent large-scale trial showed that using a cut-off point of 4.0 ng/mL would pick up 46 per cent of cancers that would occur within the next ten years with an accuracy of 91 per cent. The average age of the test group was 63 years. Among older men with benign prostatic hyperplasia (enlarged prostate) the accuracy may be as low as 54 per cent leading to many unneeded biopsies and much unwarranted anxiety. It is estimated that 75 per cent of men undergoing a prostate biopsy because they have PSA levels between 4 and 10 ng/mL do not have cancer. On the other hand, there is also a 10 per cent chance of harbouring cancer even though the biopsy shows nothing.

There are currently at least two large-scale trials underway to determine whether PSA screening is beneficial or harmful overall. However, the results of these trials are not expected until the year 2009. In the meantime Dr. Barry recommends that men aged 50 to 75 years of age (with no established risk factors) should be made aware of the availability of the PSA test and its potential harms and benefits so that they can make an informed choice about having the test. They should receive information on the following points:

  • the likelihood that prostate cancer will be diagnosed;
  • the possibilities of false negative and false positive results;
  • the anxiety associated with a positive test;
  • the uncertainty regarding whether screening reduces the risk of death from prostate cancer.

Several studies have shown that providing this information significantly reduces the proportion of men who decide to be tested.
Barry, Michael J. Prostate-specific-antigen testing for early diagnosis of prostate cancer. New England Journal of Medicine, Vol. 344, May 3, 2001, pp. 1373-77

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