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New, non-invasive
Prostate Cancer test beats PSA in detecting
Prostate Cancer
Newswise — An experimental biomarker test
developed by researchers at the University
of Michigan more accurately detects prostate
cancer than any other screening method
currently in use, according to a study
published in the February 1 issue of Cancer
Research, a journal of the American
Association for Cancer Research.
The researchers say a simple urine test that
screens for the presence of four different
RNA molecules accurately identified 80
percent of patients in a study who were
later found to have prostate cancer, and was
61 percent effective in ruling out disease
in other study participants.
This is far more accurate than the PSA blood
test currently in use worldwide, which can
accurately detect prostate cancer in men
with the disease but which also identifies
many men with enlarged prostate glands who
do not develop cancer, researchers say.
Even the newer PCA3 test, which screens for
a molecule specific to prostate cancer and
which is now in use both in the U.S. and
Europe is less precise, they say.
“Relative to what is out there, this is the
best test so far,” said the study’s lead
author, Arul Chinnaiyan, M.D., Ph.D.,
director of the Michigan Center for
Translational Pathology at the University of
Michigan.
He also says that this “first generation
multiplex” biomarker test will likely be
improved upon as researchers continue to
uncover the molecular underpinnings of
prostate cancer.
“We want to develop a test to allow
physicians to predict whether their patients
have prostate cancer that is so accurate a
biopsy won’t be needed to rule cancer out,”
Chinnaiyan said. “No test can do that now.”
Chinnaiyan and the Michigan researchers
developed the test based on their recent
finding that gene fusions – pieces of
chromosomes that trade places with each
other, causing two genes to stick together -
are common in prostate cancer, and that by
overriding molecular switches that turn off
excess growth, they may be the causative
factor in some forms of the disease.
In 2005 they identified a prostate-specific
gene called TMPRSS2 which fuses with either
ERG or ETV1, two genes known to be involved
in several types of cancer. In 2007, they
identified another five genes that fuse on
to ERG or ETV1 to cause prostate cancer.
In the current study, researchers built upon
the PCA3 test by screening for six
additional biomarkers, including TMPRSS2:ERG
as well as some molecules generally
over-expressed in prostate cancer, and some
which are over-expressed in specific cancer
subtypes.
Researchers collected urine samples from 234
men with rising PSA levels before they
underwent prostate biopsy at a University of
Michigan urology clinic. Among this group,
biopsy results confirmed a diagnosis of
prostate cancer in 138 patients; 96 patients
were cancer-free.
Correlating the urine biomarker test results
with the biopsy data, researchers found
that, in combination, four of the seven
biomarkers were significant predictors of
prostate cancer: GOLPH2, which is generally
over-expressed in prostate cancer; SPINK1,
over-expressed in a subset of these cancers;
the PCA3 transcript expression; and
TMPRSS2:ERG fusion status. Of the seven
markers, only PCA3 had been previously
reported as a diagnostic biomarker.
When tested as individual biomarkers,
GOLPH2, PCA3, and SPINK1 each outperformed
PSA, which had identified all of the men in
the study as potentially positive for
prostate cancer. “PSA was not predictive at
all,” Chinnaiyan said. “You might as well
have flipped a coin.”
The combination of the four biomarkers
achieved a specificity and positive
predictive value of greater than 75 percent,
which they found to be five percent better
than use of a PCA3 test alone, he says.
Specificity is the probability that a test
indicates a negative result if a person does
not have a disease, and the positive
predictive value is the proportion of
patients with positive test results who are
correctly diagnosed.
Chinnaiyan believes that any tests that are
developed and widely tested would first be
used to supplement a PSA blood screen.
The study was funded by the Early Detection
Research Network, Department of Defense, the
National Institutes of Health, the Prostate
Cancer Foundation, and Gen-Probe
Incorporated of San Diego.
The gene fusion technology has been patented
by the University of Michigan and licensed
to Gen-Probe Inc, which is also developing
the PCA3 screening test. Chinnaiyan is a
paid consultant to Gen-Probe.
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