A test that focuses on a blood protein produced by prostate cancer cells may improve disease diagnosis, researchers report. Levels of this protein, called prostate cancer antigen-2 (EPCA-2), appear to give an accurate picture of cancer present in the body, experts say.
"We've been able to show that blood levels of it are low in normal individuals and high in prostate cancer, and that it distinguishes between cancers that are confined to the prostate and those that have spread outside the gland," explained study lead researcher Dr. Robert H. Getzenberg, professor of urology and director of research at Johns Hopkins University's James Buchanan Brady Urological Institute, in Baltimore.
Prostate cancer is the most common malignancy in American men. There will be some 218,890 new cases in the US this year and 27,050 deaths linked to the disease, the American Cancer Society estimates. Prostate cancer is highly curable if caught early, however.
In the new study, Getzenberg's team measured blood levels of EPCA-2 in 330 men. Some of the men had an enlarged but noncancerous prostate gland, some had prostate cancer but displayed normal PSA levels, some had prostate cancer that had spread beyond the gland, and some had other cancers or medical conditions.
A specific level of ECPA-2 identified 90% of the men with cancer confined to the prostate and 98% of those in whom it had spread outside the gland. The test was negative in 97% of the men without prostate cancer, the researchers said.
That's an improvement on the standard PSA test, which provides only a rough guide in many such cases. For example, a high blood level of PSA can sometimes indicate prostate cancer, but often a biopsy reveals no such malignancy.
Conversely, a low PSA level does not necessarily mean that a man is free of prostate cancer, the researchers said.
"If this test works out, we can avoid a lot of unnecessary biopsies," Getzenberg said. About 1.3 million men in the US will have biopsies this year to find only 200,000 cancers, he noted.
"Clearly, we need further validation," Getzenberg added. "We are doing good-sized validation studies, and we are also testing the ability of the marker to identify aggressive forms of the disease."
Spotting especially life-threatening prostate tumors is "the holy grail" of diagnosis, he said. Current PSA testing cannot distinguish between cancers that will grow so slowly that they pose no danger to life and those that require quick action. The hope is that the ECPA-2 test will identify men whose slow-growing cancers make them candidates for "watchful waiting" rather than immediate surgery or other treatment.
The Hopkins team, working with researchers from the University of Pittsburgh, has licensed the test to a company, Onconome Inc. The ECPA-2 screen is a simple antibody test requiring "no special kind of technology or equipment," Getzenberg noted.
"In general, it does look very promising," Dr. Durado Brooks, director of prostate and colorectal cancers at the American Cancer Society, said of the ECPA-2 test. But much more work must be done, he added.
Brooks said the test seems to be sensitive and accurate for locating prostate cancer. "The challenge is taking it out of this isolated and rigorous setting and seeing how it performs in other laboratories and also in much larger screening-type populations," said Brooks.