New Test Checks for Prostate Cancer Return
Study Shows Experimental PSA Test Is Much More Sensitive Than Current Test
By
Salynn Boyles
WebMD Health News
Reviewed By
Louise Chang, MD
Oct. 19, 2009 -- Researchers say they have developed a highly sensitive
prostate specific antigen (PSA) test that may identify prostate cancer patients
who are likely to relapse after treatment.
In a small study, published this week in the journal PNAS Early
Edition, the test proved to be 300 times more sensitive than commercially
available PSA tests.
Northwestern University researcher Chad A. Mirkin, PhD, helped develop the
test and co-founded the company that hopes to market it.
He tells WebMD the molecular approach, based on a science known as
nanotechnology, may be able to tell men if their prostate cancers will come
back after surgery years earlier than current tests can.
"The first thing our study proved is that almost everybody has a measurable
level of PSA after the prostate is removed," he says. "We haven't been able to
measure this with the tests we have now."
While the usefulness of measuring PSA in screening men for prostate cancer is now questioned, there is little argument that rising PSA levels following
treatment predict recurrence.
But PSA is usually undetectable for several years after surgical removal of
the prostate, even in men who will eventually relapse, Mirkin says.
"If you measure levels after surgery with the conventional tests, PSA will
be zero," he says "Men typically have to wait five to seven years to know if
their cancers will return."
How the Test Works
The test developed by Mirkin and colleagues uses tiny gold nanoparticles to
seek out previously undetectable levels of PSA in a patient's blood.
The researchers tagged the nanoparticles with thousands of strands of DNA,
along with antibodies that recognize PSA.
For every PSA molecule captured, hundreds of thousands of DNA strands were
released, Mirkin says.
In the newly published study, stored serum samples collected from 18
prostate cancer patients who had their prostates surgically removed were
analyzed using both the nanoparticle-based test and a commercially available
test.
The ultrasensitive test was able to detect rises in PSA earlier than the
commercially available test in several of the men.
Mirkin tells WebMD that a study involving 250 surgically treated patients is
under way to confirm the findings.
He and co-authors C. Shad Thaxton, MD, PhD, and Norm D. Smith, MD, are
shareholders in the company Nanosphere Inc., which plans to seek FDA approval
for the test.
Second Opinion
American Cancer Society spokesman Durado Brooks, MD, calls the findings from
the new study "interesting but preliminary."
He says even if the larger study confirms that the molecular test can
reliably identify patients whose prostate cancers will recur after surgery, the
clinical benefit of this is not clear.
That is because there are not many good treatment options for men with
recurrent prostate cancer.
"We know that a rising PSA after treatment portends recurrent disease, but
we don't know if finding that rise now or three years from now will make a
difference in outcomes," he tells WebMD.
SOURCES: Thaxton, C.S. PNAS Early Edition.
Chad A. Mirkin, PhD, director, International Institute of Nanotechnology; professor of chemistry, Northwestern University, Chicago.; co-founder, Nanosphere Inc., Northbrook, Ill.
Durado Brooks, MD, director of prostate and colorectal cancer programs, American Cancer Society.
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