PSA Test Has Shortcomings, Study Shows
Value of Prostate Cancer Test Has Eroded Over the Years, Researchers Say; More Biopsies on the Horizon?
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PSA Over Time
Scherr and colleagues reviewed 1,607 patients who had prostate biopsies done at Cornell's New York Presbyterian Hospital between 1993 and 2005, dividing the patients into three groups based on when biopsies were performed (1993-1997, 1998-2001, and 2002-2005).
They found that the number of biopsies performed, the percentage of positive biopsies showing cancer, and patient ages did not change significantly over time.
But there was a significant decrease in the average PSA level among biopsied patients and an increase in the number of core samples taken during biopsies.
Over the entire study period, the positive biopsy rate in men with PSA levels between 2 and 4 and normal prostate exams was not significantly different from that of men with higher PSA levels and normal prostate exams.
The study is published in the March 15 issue of the American Cancer Society (ACS) journal Cancer.
Scherr tells WebMD that whether the PSA was as low as 2.5 or as high as 10, the likelihood of finding cancer was about the same in the biopsied patients.
"So the utility of using PSA to weed out who does and does not need a biopsy has really been lost given the fact that the prostate cancers we are finding tend to be smaller than they were," he says.
Should We Biopsy Everyone?
The Cornell researchers conclude that better molecular markers are needed to screen for prostate cancer.
"Given the fact that PSA has far less predictive value than it had in the early '90s, the next question is, can we replace it?" Scherr says.
One potential approach, he adds, is to perform prostate biopsies on all men when they reach the age of 50, in the same way that colonoscopy is recommended to look for colon cancer.
"I'm not recommending this, but we are beginning to look at this question," he says. "If the biopsy is the ultimate arbiter, maybe we should move in the direction where we biopsy everyone."
ACS Director of Screening Robert A. Smith, PhD, says more biopsies would likely lead to the detection of more very early-stage prostate cancers.
"PSA is an imperfect test for the early detection of prostate cancer, but it happens to be the best one we have at the moment," he says. "Because of the uncertainties, leading cancer organizations, including ACS, recommend that men discuss the pros and cons of this test with their doctors."
PSA researcher Andrew Vickers, PhD, tells WebMD that PSA testing is useful in predicting, decades before the fact, which men will develop prostate cancer.
The Memorial Sloan-Kettering Cancer Center statistician co-authored a study published last month suggesting that a single PSA test taken at age 50 or before is a very strong predictor of who will have prostate cancer up to 25 years later.