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Prostate Cancer Test Works As
Well For Black Men, Study Shows
A new twist on the standard way to predict prostate cancer risk appears
to offer African American men a much needed, improved accuracy in detecting
the disease.
A review of data from a recent nationwide trial of the free prostate
specific antigen test (fPSA) - a variation on the traditional PSA test
- shows the new test proves as accurate in revealing cancer risk in African
American men as it is in Caucasians.
"It also shows that many African-Amercian men could be spared the expense
and trauma of prostate biopsies," says Johns Hopkins urologist Alan W.
Partin,M.D., Ph.D., co-leader of the research team. "Nearly 75 percent
of the prostate biopsies that both black and white men get are unnecessary,"
says Partin.
A report on the study at Johns Hopkins and six other U.S. medical
centers appears in the March issue of the journal Urology.
The fPSA, a more sensitive text for cancer risk than the standard PSA
test men get as part of routine physicals, won Food and Drug Administration
approval two years ago, based on national trial of 773 men who both had
test as well as prostate biopsies. This earlier trial showed that
fPSA detected 95 percent of the cancers. It also reduced unnecessary
prostate biopsies that men would have routinely after the standard PSA
test.
A variety of races took part in this original trial, which compared
the two tests as detectors of prostate cancer. "But because the trail
was composed mostly of Caucasian men," Partin says, "we saw a need to reanalyze
the data specifically for the subset of African-Americans, who are at far
higher risk."
The new analysis shows no significant differences exist between blacks
and whites in the performance of the fPSA test.
Since FDA approval, the fPSA, is becoming a follow-up test for men whose
PSA falls in a "diagnostic gray zone" of moderately elevated levels --4/
to 10 ng/ml. The risk of prostate cancer in this group is 25 percent
in Caucasians and 30 to 50 percent in African-American men. Prior
to development of the free PSA test, men in the "gray zone" had to undergo
biopsies, often repeated. Prostate biopsies are expensive - around
$1,000 - and may be painful or psychologically traumatic, says Partin.
"African-American men have the highest rate of prostate cancer in the
world," says Partin. It's approximately one third greater for white
males. They also have higher PSA values when the cancer is diagnose.
"No one understands the precise reason for this," he adds, "though theories
abound. It's probably a combination of biological and environmental
factors."
PSA is an enzyme made by all prostate cells normally secreted into semen.
Both cancer and a number of benign conditions can change the architecture
of the prostate gland so the enzyme "gets out the back door" and into the
bloodstream. Once there, PSA can exist in two forms - one that's
free floating and another that's bound to proteins. The standard
PSA measures both forms. The free PSA test looks at the ratio of
the free form to the total.
"For some reason," says Partin, "having a higher amount of free PSA
is linked with a lower risk of prostate cancer."
The study was funded by a grant from Hybritech Incorporated, San Diego,
Calif.
Other researchers in the study were Patrick C. Walsh. M.D., professor
and director of the Department of Urology at John Hopkins, William J. Catalona
and Kathy Naughton of Washington University in ST. Louis, Kevin M. Slawin
and Peter Scardino of the Baylor COllege of Medicine, Houston, Michale
K. Brawer and Paul H. Lange of the University of Washington, Seattle, Robert
C. Flanigan of Loyola University, Maywood, Ill., Anup Patel and Jean B.
deKernion of UCLA, Jerome P. Richie of Harvard, and Paula C. Southwick,
Kathleen G. Loveland, Robert E. Parson and Gail H. Gasior of Hybritech
Incorporated, San Diego.
Neither of the Hopkins researchers hold and financial interest in Hybritech
or its subsidaries. Alam W. Partin is the editor of Urology.
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