New Test Checks for Prostate Cancer Return

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.