For many men, a routine PSA blood test to screen for prostate cancer has become an annual ritual. Now the developer of the test says it can’t be relied on for this purpose, and has led to overly zealous treatment of men with prostate enlargement.

Dr. Thomas A. Stamey at Stanford University first reported in 1987 that levels of PSA in the blood could be used as a marker of prostate cancer.

“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,” Stamey notes in a university press release. Standard units of measurement of PSA are nanograms per milliliter (ng/mL) of blood.

Stamey’s group found that the average size and invasiveness of prostate cancers have been dropping over the past two decades, to the point that the cancers being discovered may not be clinically meaningful.

The investigators examined tissue from 1317 prostates removed at Stanford since 1983. During the first 5-year period, 91 percent of cancers were obvious on digital rectal examination (DRE), and average volume of the cancer was 5.33 cc. Between 1999 and 2003, these values had declined to 17 percent and 2.44 cc.

Also, the degree to which the tumor had penetrated the wall of the prostate dropped from an average of 1.54 to 0.22 centimeters between the two periods.

What has happened, Stamey and his colleagues suggest in the Journal of Urology, is that prostate cancer is being over-treated, given that most men will develop the disease if they live long enough and the fact that death from prostate cancer is uncommon in elderly men.

The authors conclude that the extensive use of PSA screening is not warranted. Instead, they recommend “careful palpation of the prostate” by DRE - since cancers found in this way “almost always require some form of treatment.”

SOURCE: Journal of Urology, October 2004.