MONDAY, March 10 (HealthDay News) -- Changes in medical practice
have undermined the value of the prostate-specific antigen (PSA)
test as a diagnostic tool for prostate cancer, a new study
asserts.
However, that assertion was immediately challenged by other
experts in the field.
The American Cancer Society recommends annual screening for
prostate cancer for most men after age 50. The screening is done in
two steps: a digital rectal exam, followed by a blood test for PSA,
a protein produced by the prostate gland.
"In men with an abnormal digital rectal examination, it [the PSA
test] still is very predictive," said study author Dr. Douglas S.
Scherr, clinical director of urological oncology at Weill Cornell
Medical Center in New York City. "For men with a normal digital
rectal examination, it has lost the predictive accuracy it had in
the 1990s."
For those men, exact PSA readings matter less, because doctors
are doing more biopsies now and are using improved biopsy
techniques, Scherr explained. His report was expected to be
published in the April 15 issue of
Cancer. In a retrospective analysis, his team looked at
1,607 prostate biopsies performed at Weill Cornell between 1993 and
2005, and uncovered several trends.
In the 1990s, biopsies generally were limited to men with PSA
readings higher than 4 nanograms per milliliter of blood. Later,
they were often done when the PSA levels were between 2.5 and 4,
Scherr said.
"In the early and mid-90s, we used six needles when we did a
biopsy," he said. "Now, we stick in 14. Taking more cores and doing
biopsies at lower PSA levels has allowed us to keep the prostate
cancer detection level steady. If we kept the PSA level at 4 rather
than at 2.5, the cancer detection rate would have fallen
rapidly."
Increased awareness of prostate cancer has also changed the
screening picture, Scherr said. "You almost never have an abnormal
rectal examination these days," he said.
There is a need to develop new biomarkers for prostate cancer
beyond PSA, Scherr said. "Should a man when he turns 50 have a
biopsy?" he said. "It is certainly an important question that needs
being looked at."
But the study merely "makes a statistical point about an unusual
population," said Andrew Vickers, a statistician whose title at
Memorial Sloan-Kettering Cancer Center in New York is attending
research methodologist.
"It apples to men who have regular screening," Vickers said. "It
doesn't apply to men who haven't been screened. For those men, the
PSA test might be more accurate."
And the study is misleading because of information it doesn't
contain, said Dr. Ian M. Thompson, chairman of urology at the
University of Texas Health Science Center at San Antonio.
The study includes only men on whom biopsies were done, Thompson
said. "If you don't biopsy something, you don't know if you have
cancer or not," he said. "The study is informative only of men who
had biopsies. There is nothing in it about the criteria they used
to recommend biopsies."
Risk factors for prostate cancer, such as ethnicity, age and
family history, are not mentioned in the study, Thompson added.
"You don't know anything about the people in their practice who
never had a biopsy," he noted.
The PSA test has flaws, Thompson acknowledged. Most notably, it
is unable to distinguish between prostate cancers that will grow so
slowly that they do not endanger life and those that are aggressive
enough to kill.
"But of all the tools we currently have, the PSA test is
valuable," he said. "People dealing with other kinds of cancer wish
they had a blood test like PSA."
More information
You can learn about the diagnosis and treatment of prostate
cancer from the
National Cancer Institute.
