Leading Prostate Cancer Test 'Clinically Useless'
PSA test doesn't detect tumor's severity, Stanford University study says
FRIDAY, Feb. 1, 2002 (HealthDayNews) -- The leading test to detect prostate cancer is "clinically useless" at determining the size or severity of a man's tumor, and is only of "limited" value at predicting cure rates from surgery to remove the diseased gland, a new study says.
The test, which measures a blood enzyme called prostate-specific antigen (PSA), is likelier to find benignly enlarged prostates and prompt overly aggressive treatment, according to the scientists who conducted the study.
The study, which appears in the January issue of the Journal of Urology, "is quite a disappointment," says Dr. John McNeal, a Stanford University pathologist and a co-author of the paper.
"We used to think [PSA testing] was good. But what we would like it to tell us is whether a PSA that is not much elevated is elevated because of [normal prostate growth] or whether it's elevated because of prostate cancer." And the protein, at least at moderate levels, can't do that, McNeal says.
Dr. Peter Albertsen, chief of urology at the University of Connecticut in Farmington, says the study "is not going to knock PSA screening off the map by any means."
However, Albertsen adds, PSA testing is undergoing a crisis of confidence similar to that of screening mammography, another exam whose value has come under questioning.
"I think there's enough tantalizing evidence to think" that routine PSA screening saves lives, Albertsen adds. But there's not enough evidence to be sure.
Almost 190,000 American men are diagnosed annually with prostate cancer, and 30,000 will die from it, according to the American Cancer Society. PSA testing is widespread in men over age 50, but no study has proved that it saves lives by helping doctors identify prostate tumors when they're still curable.
One reason: prostate cancer grows glacially. So while most men will die with cancer of the gland, relatively few will die of it. Aggressive treatment of slowly growing tumors may therefore cause more harm than good, some experts argue.
In the latest study, Dr. Thomas Stamey, a Stanford University urologist, and his colleagues studied the relationship between PSA scores in 875 men who underwent radical prostate surgery, in which the gland was completely removed, between 1984 and 1997.
Stamey's group analyzed PSA readings taken from many of the men both before and after their operation.
The largest tumors did produce extremely elevated PSA levels, topping 22 nanograms per milliliter of blood. Scores of more than 9 ng/ml were somewhat associated with aggressive disease, as measured by standard gauges of malignancy.
But for PSA values between 2 and 9 ng/ml, the culprit was often not cancer but benign prostatic hypertrophy (BPH), or normal swelling of the gland.
Nor did PSA testing predict cure rates: Surgery success was the same for men whose pre-operation PSA was lower than 4 ng/ml as it was for those with a score of 10 ng/ml.
The PSA enzyme is secreted by cells in the prostate, and mildly elevated values often reflect a larger than normal gland. BPH is as common as cancer, a fact many men don't realize.
Scientists have been trying to tweak the PSA test to make it more reliable, but whether these new techniques will be more sensitive to cancers remains a mystery. In fact, PSA is a misnomer, since the enzyme is secreted not only in the prostate but in the breast as well.
What To Do
Every man has a PSA level, and any score between one and four could be totally normal, McNeal says. The tricky part comes in deciding what to do if the test comes back between 7 and 8. Despite his group's findings, McNeal says he would probably undergo a biopsy if his own PSA test were in that range.
And for more on benign prostate swelling, try the National Institute of Diabetes and Digestive and Kidney Diseases.