In the first clinical study of a new blood protein associated with prostate cancer, researchers have found that the marker, called EPCA or early prostate cancer antigen, can successfully detect prostate cancer in its earliest stages. At the same time, the marker successfully avoids the problem of false positive results that plagues prostate-specific antigen (PSA) testing.
Study results appear in the May 15, 2005, issue of Cancer Research. The lead author is Robert H. Getzenberg, Ph.D., professor of urology and director of research at the James Buchanan Brady Urological Institute at Johns Hopkins.
The traditional two-step approach of PSA testing and digital rectal examination has helped doctors identify prostate tumors early, while the cancers can still be cured. But PSA testing, like many disease-screening procedures, misses some cases of cancer and in other cases erroneously highlights noncancerous conditions.
"This new blood test, when coupled with PSA screening, may help reduce the number of both unnecessary biopsies and undetected prostate tumors," said Getzenberg, In addition to being highly sensitive to prostate cancer, the EPCA test is also very specific to it, meaning that other cancers and benign prostate conditions are not detected, thus boosting doctors' confidence that a positive EPCA test is really a sign of prostate cancer, added Getzenberg.
"Once this test is refined and approved for general use, it will have an impact on the detection and treatment of prostate cancer," said Getzenberg.
For the current study, Getzenberg and colleagues developed a simple test that would detect EPCA in the blood and then measured the EPCA levels in 46 patients, including those with prostate cancer (12 patients), bladder cancer (six patients), colon cancer (two patients), kidney cancer (one patient), spinal cord injury (seven patients) and noncancerous prostate inflammation (two patients), and 16 healthy individuals. The study was conducted at the University of Pittsburgh while Getzenberg was a member of its faculty.
The researchers found that EPCA levels were high in 11 of 12 prostate cancer patients (92 percent) and low in all of the healthy individuals. Only two bladder cancer patients and none of the other patients had elevated EPCA levels, suggesting that for this study, the test was correct 94 percent of the time. For comparison, only one-quarter of patients who undergo biopsies because they have elevated PSA values are actually positive for prostate cancer, while as many as 15 percent of those with low PSA values were found to have prostate cancer as detected by biopsy, according to Getzenberg.
Larger clinical trials are under way to further refine the EPCA test, to make it more sensitive so it can pick up even the smallest traces of the marker, and to verify its usefulness for detecting prostate cancer in a larger sample of patients, said Getzenberg.
Prostate cancer is the most common type of cancer found in American men. The American Cancer Society estimates that there will be approximately 232,090 new cases of prostate cancer in the United States in 2005, and 30,350 men will die of this disease.
Funding for the study was provided by Tessera Inc. Other authors on the report are Barbara Paul, Rajiv Dhir, Douglas Landsittel and Moira Hitchens, all of the University of Pittsburgh.
Robert Getzenberg is a paid consultant to and received an unrestricted research grant from Tessera Inc. Under separate agreements between the University of Pittsburgh and Tessera and the Johns Hopkins University and Tessera, Getzenberg is entitled to a share of royalty payments to the universities on sales of licensed products. The EPCA test is the subject of the license agreement between the University of Pittsburgh and Tessera.
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