Strong Doubts About PSA Testing

Following a study showing that the prostate-specific antigen (PSA) test as a screen indicates nothing more than the size of the prostate gland, researchers have declared that the test is all but useless for predicting cancer risk.

In the study, the researchers looked at prostate tissues collected over 20 years and found that the PSA test is actually not a useful predictor of the amount or severity of prostate cancer. Elevated levels of PSA instead reflect benign prostatic hyperplasia, a harmless increase in prostate size.

"The PSA era is over in the United States,” said lead author Thomas Stamey, M.D., professor of urology at Stanford University School of Medicine (Palo Alto, CA, USA; www.med.stanford.edu). "Our study raises a very serious question of whether a man should even use the PSA test for prostate cancer screening anymore.” The new findings are to appear in the October 2004 issue of the Journal of Urology.

Dr. Stamey noted that the tumors encountered 20 years ago were generally so large they generated PSA levels high enough to provide a reasonably good measure of cancer severity. Now that screening is more commonplace, many cancers are being caught earlier and are usually smaller--not generating enough PSA to be a good indicator of severity. Still, the American Cancer Society estimates that nearly a quarter of a million cases of prostate cancer will be diagnosed in the United States alone this year, and one in six men will be diagnosed with the disease at some point in their lives.

However, the risk of dying from prostate cancer is very low compared with lung cancer, for example. Only 226 men out of every 100,000 over the age of 65 dies of prostate cancer, which is a rate of 0.003%.

Men whose PSA levels are above 2 ng/ml frequently undergo biopsy, which will almost always find cancer, but this does not necessarily mean that prostate removal or radiation treatment is required. "What we didn't know in the early years is that benign growth of the prostate is the most common cause of a PSA level between 1 and 10 ng/ml,” noted Dr. Stamey.

Dr. Stamey pointed out that the PSA test is still very useful for monitoring patients following prostate removal as an indicator of residual prostate cancer that has spread to other parts of the body. "Our job is to stop removing every man's prostate who has prostate cancer. Some men need prostate treatment but certainly not all of them.”

This raises the question of what, then, is the best course for detecting prostate cancer? Dr. Stamey recommends a yearly digital rectal exam for all men over 50. "If a cancer is felt in the prostate during a rectal examination, it is always a significant cancer and certainly needs treatment.” Unfortunately, even large cancers often cannot be felt during a rectal exam. Dr. Stamey and colleagues are working on finding a blood marker that could indicate more aggressive forms of the cancer that can invade the body.




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