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New Blood
Test greatly reduces False-Positives in
Prostate Cancer Screening
Newswise — A new blood test used in
combination with a conventional
prostate-specific antigen (PSA) screening
sharply increases the accuracy of prostate
cancer diagnosis, and could eliminate tens
of thousands of unneeded, painful, and
costly prostate biopsies annually, according
to a study led by researchers at Dana-Farber
Cancer Institute.
At the annual meeting of the American
Society of Clinical Oncology in Orlando,
Fla., William K. Oh, M.D., and Robert W.
Ross, M.D., will report that the six-gene
molecular diagnostic test, when combined
with a PSA test, accurately detected
prostate cancer more than 90 percent of the
time.
Earlier studies suggest that the
conventional PSA test is 60-70 percent
accurate in detecting cancer.
The findings (abstract #5052) will be
discussed at a poster session on Sunday, May
31, 8-11 a.m., Level 2, W230A.
Men who are found to have elevated levels of
PSA in routine screening tests are often
referred for a biopsy of the gland to check
for tumors. Nearly two-thirds of biopsies
performed -- a painful procedure with some
risk of complications -- do not find any
cancerous cells.
This high rate of "false positive" PSA test
results underscores the need for a more
accurate method for detecting prostate
cancer, said Oh, who is the clinical
director of the Lank Center for
Genitourinary Oncology at Dana-Farber.
The two-year study involved 484
participants. The group comprised 204 men
with known prostate cancer, 110 men with
benign prostatic hypertrophy (BPH), and 170
healthy men in a control group. (BPH can
elevate PSA levels in the blood, which often
leads to a biopsy to rule out prostate
cancer.)
These groups were split into age-matched
training and validation sets.
The researchers sought to measure the
accuracy of a six-gene whole blood RNA
transcript-based diagnostic test developed
by Source MDx in Boulder, Colo., both in
terms of its sensitivity (the ability to
detect prostate cancer) and specificity (the
ability to identify people who don’t have
prostate cancer).
Source MDx researchers developed the test
after initially working with a set of 174
candidate genes whose activity was compared
in the different study groups.
They narrowed the pool down to just six
genes that, as a group, were highly
sensitive in predicting which patients had
prostate cancer and which were normal.
The study found that "the six-gene model was
more accurate than PSA alone at predicting
cancer if you had it and no cancer if you
didn't," said Oh.
The test's accuracy improved even more when
PSA measurements were added. Combined, the
two tests achieved a diagnostic accuracy of
more than 90 percent in specificity and
sensitivity and eliminated most of the
false-positives yielded by the PSA test.
Based on these findings, the researchers are
planning to conduct a larger, multicenter
clinical trial involving approximately 1,000
men to determine if the findings remain
valid.
"These findings are very encouraging and
suggest that this new test could spare tens
of thousands of men from undergoing an
unnecessary biopsy," Oh said.
"However, until we can verify our findings,
it is important to recognize that the PSA
test, despite its limitations, is still the
best test available for diagnosing prostate
cancer at this time."
The study was funded in part by Source MDx
and a Prostate Cancer SPORE grant at
Dana-Farber/Harvard Cancer Center.
Dana-Farber Cancer Institute (www.dana-farber.org)
is a principal teaching affiliate of the
Harvard Medical School and is among the
leading cancer research and care centers in
the United States.
It is a founding member of the
Dana-Farber/Harvard Cancer Center (DF/HCC),
designated a comprehensive cancer center by
the National Cancer Institute.
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