MONDAY, May 10, 2004 (HealthDayNews) -- The PSA test, long the gold standard for deciding who should have a biopsy for prostate cancer, may have outlived its usefulness for the most part.
Stanford University researchers say PSA (prostate specific antigen) levels bear little relationship to the severity of a cancer these days. They presented their finding May 9 at the American Urology Association's annual meeting in San Francisco.
"We need to recognize that PSA is no longer a marker for prostate cancer," said study author Dr. Thomas A. Stamey, a professor of urology at Stanford University School of Medicine. "We urgently need to find a new marker for prostate cancer, and that marker must be proportional to how much cancer you have."
"We have been so thorough and effective in screening for prostate cancer over this 20-year period that PSA no longer has a relationship to prostate cancer," Stamey said. "Because we all develop the cancer, we're now removing prostates from men whose cancer is so small that they do not need the procedure. We're finding all these little cancers that are never going to be a danger to the patient."
"In smaller cancers, the PSA test is not relevant anymore," Stamey explained. "You might as well biopsy a man because he has blue eyes."
PSA is a protein produced by the cells of the prostate gland. Because blood levels of the antigen tend to rise as the gland enlarges, it has been used for years as a test of whether a person needs a biopsy for cancer. The test, however, is not foolproof.
"People's perceptions [are] that if your PSA is a certain level, you're very likely or you do have prostate cancer, and that is incorrect," said Dr. Mark Soloway, chairman of the department of urology at the University of Miami School of Medicine.
"The PSA test is a very good test. It's not a perfect test, especially in younger men," added Dr. Jay Brooks, chief of hematology/oncology at the Ochsner Clinic Foundation in New Orleans.
To see how the efficacy of the PSA test might have waned, researchers in Stamey's lab reexamined every prostate that had been removed since 1983 (1,317 of them) and compared the size of the cancer with blood PSA levels. None of the cancers had been treated with chemotherapy, radiation, or hormones before surgery.
Each cancer was rated on eight or 10 different parameters thought to indicate how aggressive the cancer was, including the size of the tumor and its grade.
Stamey then divided the samples into four five-year periods to see what had happened to the qualities of the cancers over time.
"What we showed was that in the first five years, the cancers were related to the level of serum PSA," Stamey said. "Then in the next five years, they were still bad but not as bad as the first five years. Then in the third five-year period, they were better and better. And in the last five years ending Jan. 1 of this year, the cancers were so small they had no relationship to serum PSA."
Twenty years ago, 80 percent of cancers were detected by digital rectal examination; only 20 percent of cancers are now detected that way, Stamey explained.
Instead, PSA levels today are driven by benign enlargement of the prostate, a condition that does not usually require surgery.
The concept that the PSA test is not foolproof is not an entirely new one. "The point is well taken that in microscopic disease, the volume of cancer is clearly overshadowed by the volume of noncancer, so that the cancer cannot be the cause of the elevated PSA," said Dr. John Phillips, physician-in-charge of urologic oncology at Beth Israel Medical Center in New York City.
The question now is what can replace it. "People are trying to find other ways of finding cancer," Phillips added.
As a matter of fact, University of Pittsburgh researchers who presented at the same conference reported that additional testing for a protein called early prostate cancer antigen (EPCA) might mean prostate cancer could be detected as many as five years earlier than with just the PSA test.
"We would like a perfect test that would only find biologically significant cancers," Soloway said. "Today we can't distinguish between those with indolent cancer and those whose cancers threaten their life. We need another way. That's going to be a difficult task."
In the meantime, the American Urological Association issued a statement that, for the time being, the PSA test in combination with a digital rectal exam and a full medical history is the best way to determine when a biopsy might be necessary.