WASHINGTON, Jul 28, 2003 (United Press International via COMTEX) -- Millions of men across America and their families rely on a blood screening test to pick up any potential signs of prostate cancer, but new research continues the controversy surrounding the test.
Researchers from a trio of Boston-area institutions -- Brigham and Women's Hospital, the Dana-Farber Cancer Institute and the Harvard School of Public Health -- re-evaluated the well-established and widely used test that looks for prostate specific antigen, or PSA, a protein produced by the prostate gland that rises if cancer is present. Their findings suggest PSA screening might be less effective than previously thought.
In a surprise finding, the researchers found the PSA test "might be missing as many as 82 percent of cancers," Karen Kuntz, a co-author on the study, told United Press International. "We don't know if PSA testing is a good idea or not. We don't know if it's effective, if it reduces cancer mortality."
At issue is the threshold level for PSA screening, which currently is noted by a rating of 4.0, the cut-off point used to determine whether a biopsy is recommended. A test result of 4.0 or higher usually indicates a biopsy is necessary and, according to the American Cancer Society, a 4.0 PSA result predicts a 25 percent chance of prostate cancer.
The Boston scientists now argue that lowering the threshold level for PSA, particularly for younger men -- meaning under age 60 -- could detect more tumors. Their assertion is based on computer calculations.
The team looked at data on 6,691 men who underwent PSA screenings between 1995 and 2001 at Washington University School of Medicine in St. Louis. Of this group, 705 men or 11 percent underwent biopsies. Researchers created a computerized graph to determine how effective PSA screening was among this group.
Based on the computer's calculations, PSA screening missed more than four out of five prostate cancer tumors in men ages 60 and under and as many as 65 percent among men older than 60. As the researchers reported in the July 24 issue of The New England Journal of Medicine, lowering the threshold to 2.6 would double the cancer-detection rate among younger men without significantly increasing the number of false-positive PSA test results.
Kuntz said the researchers were not expecting those kinds of numbers. "We were surprised," she admitted. "It is based on a statistical model so it might be a little on the high side or it could be a little on the low side. It's hard to know. It's up to the medical community to decide what the trade-offs should be. You will miss cancer. It's not a perfect test."
In an editorial accompanying the article, Fritz Schroder and Ries Kranse of Erasmus Medical Center in Rotterdam, Netherlands, said there was no conclusive data to show PSA screening actually reduced the risk of death from prostate cancer without compromising the quality of a man's life. Prostate cancer treatments, such as surgery and radiation, can deeply impair a man's quality of life and lead to impotence, and urinary and bowel incontinence.
Dr. James Cummings, chief of the urology division at St. Louis University Medical School said the study's findings confirm what physicians already had suspected about the PSA threshold, and he suggested it could be adjusted based on age.
"Most of us have always known -- or suspected, perhaps -- that in a 40-year-old man (with undiagnosed prostate cancer), that number, say 4, might even be lower, like 3 or 2.5," Cummings said. "What this study shows is that we were probably right in that estimate, particularly in younger men. The real question from this data needs be addressed in the long term. If we lower the biopsy threshold, are we increasing the number of prostate cancers detected or are we detecting the same numbers and just detecting them earlier?"
Cummings also questioned the 82-percent figure quoted in the study. "I'm not sure that's an accurate number," he said.
According to the National Prostate Cancer Coalition, a man's chance of developing the disease during his lifetime is about one in six. Race also can play a factor. For example, African-American men have a 60-percent higher incidence of prostate cancer than white males -- and double the mortality rate. The NPCC maintains that PSA testing saves lives, although the threshold might need to be adjusted based on the patient's age and ethnic background, because age and race are risk factors.
Almost 29,000 men die of the disease in the United States every year.
Dr. Mark S. Litwin, a professor of urology and public health at the University of California, Los Angeles, Jonsson Cancer Center, said many prostate cancers are low-grade and unlikely to develop to an aggressive, life-threatening stage.
"The real challenge is not for us to diagnose more prostate cancers, but to diagnose the prostate cancers that need to be treated," Litwin told UPI. "Simply lowering the threshold to 2.5 is so simplistic that I don't think it's helpful. The vast majority of prostate cancers aren't harmful to patients because they never declare themselves."
Litwin said the 82 percent figure "makes it overblown" and is the "sensationalistic value" of the study.
The problem with PSA screening, Litwin said, is not that it's missing cancers. "It's a very accurate test," he said. "The problem is it's too accurate -- it's too powerful."
Copyright 2003 by United Press International.