New Blood Test For Prostate Cancer

WebMD April 26,2007

An experimental blood test for prostate cancer seems to work better than the current PSA test — and can tell whether the cancer is spreading.

The new test looks for a protein called EPCA-2, early prostate cancer antigen 2. Unlike the PSA (prostate-specific antigen) protein on which the current PSA test is based, this protein isn't found in normal prostate cells. Instead, EPCA-2 occurs in relatively large amounts only in prostate cancer cells.

The test is being developed by Robert H. Getzenberg, Ph.D., director of urology research at Johns Hopkins University's Brady Urological Institute. Getzenberg began the work while still at the University of Pittsburgh; the test has been licensed to the Seattle biotech firm Onconome Inc.

"We wanted to find something that really identified people with prostate cancer and not people with enlarged or infected prostates," Getzenberg tells WebMD. "This is as close to cancer specific as we could find. We found it is very unique. It is 97 percent specific, meaning that if you test positive there's only a 3 percent chance you don't have prostate cancer."

In the new study, Getzenberg's team measured blood levels of EPCA-2 in 330 men. Some of the men had an enlarged but non-cancerous 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 percent of the men with cancer confined to the prostate and 98 percent of those in whom it had spread outside the gland. The test was negative in 97 percent of the men without prostate cancer, the researchers said.

Getzenberg has a financial interest in the test. But experts who do not stand to gain from the test agree that it has enormous potential.

Otis Brawley, M.D., chief of the solid tumor service at Emory University's Winship Cancer Institute, calls the test "important" and predicts it will be widely used.

Charles A. Coltman Jr., M.D., associate chairman for cancer control and prevention at San Antonio's Southwest Oncology Group, calls the findings "striking" and "remarkable," although he warns that the test has been tried out on only a small number of patients.

Ganesh Palapattu, M.D., assistant professor of urology at the University of Rochester, agrees that more studies must be done. But he tells WebMD that the test is a big step toward the "Holy Grail of prostate cancer detection: not so much identifying men with prostate cancer, but identifying men with prostate cancer who have aggressive disease."

"This not only helps tell whether you have prostate cancer, but what kind of prostate cancer you have," Getzenberg says.

Getzenberg and colleagues report early studies of the EPCA-2 test in the April issue of the journal Urology.

EPCA-2 Test Beats PSA

Nobody is entirely happy with the current PSA test for prostate cancer. A man without prostate cancer can have high PSA levels. A man with advanced prostate cancer may have very low PSA levels.

Getzenberg's team tried out the EPCA-2 test on blood samples from several different groups of people. Some were known to have early prostate cancer or late prostate cancer, and some had other kinds of cancer. Some had enlarged prostates, but not cancer. Some were women, who have no prostate gland. And some were healthy men with normal PSA levels.

Both in terms of detecting cancer when it was actually there (sensitivity), and in terms of not detecting cancer when it wasn't actually there (specificity), the EPCA-2 test beat the PSA test.

More importantly, it beat the PSA test in predicting whether prostate cancer already had spread outside the prostate gland. When that has happened, standard treatments for prostate cancer — radical prostatectomy (surgery to remove the prostate) and brachytherapy (tiny radioactive seeds implanted in the prostate) — fail to cure.

"I predict that within the next year, this test is going to be widely used to find the guy who has prostate cancer and who, if he got radical prostatectomy, would relapse very quickly," Brawley tells WebMD. "It is going to say to this guy, 'Skip the unnecessary surgery and get pelvic radiation and hormone treatment now.'"

Getzenberg says it will be at least two years before the test is "out on the street" with FDA approval. All of the experts who spoke to WebMD agree that large-scale screening tests will be needed before it's known exactly how well the test works.

"What we really need to know is how this test behaves in all comers, when we don't already know whether the men being tested have prostate cancer," Palapattu says. "It would also be important to identify men with high risk of prostate cancer vs. low risk of prostate cancer, and to test men after prostate surgery to see whether it can predict cancer recurrence."

When, and if, the EPCA-2 test is approved, men will still need better prostate cancer tests.

"At least a third, maybe two-thirds of guys with localized disease have cancer that will never leave the prostate and never bother them," Brawley says. "This new test is not going to help those guys who get treated for prostate cancer but shouldn't. I hope there will be help for these men soon."