A Promising New Screen for Prostate Cancer

By Katherine Hobson
Posted 4/26/07

The prostate-specific antigen (PSA) test, used to screen for prostate cancer, is imperfect. It often flags conditions that turn out to be benign, resulting in unnecessary biopsies for more than a million men every year, and it misses other cases of cancer entirely. So the search is on for a better way to find the disease and avoid needless bother and pain for those who don't have it.

Researchers at the Johns Hopkins University School of Medicine think they have a promising candidate. In the April issue of Urology, they report that they've found another marker in the blood, a protein called EPCA-2, which in a preliminary study did a far better job than the PSA at pointing to real cancers and ignoring noncancers. It also predicted whether a man's cancer was confined to the prostate gland or had spread beyond it, a key piece of information in deciding how to treat it. While there have been other potential improvements over the PSA, "only a handful have shown this type of results," says Robert Uzzo, a urologic oncologist at the Fox Chase Cancer Center in Philadelphia who wasn't involved with the study.

Robert Getzenberg, director of urology research at the Brady Urological Institute at Hopkins and lead author, cautions that it will take more extensive trials to nail down whether EPCA-2 might someday become a screening test that either complements or replaces the PSA test. In this study of 385 men, the test was negative in 97 percent of those who didn't have cancer, which means only 3 percent of men got false positive results. (Meantime, PSA test results cause 1.6 million men to have biopsies every year, only 20 percent of whom actually have cancer.) It was also adept at distinguishing between cancer and enlarged prostate: Seventy-seven percent of men with the benign condition had a negative EPCA-2 test. And it didn't miss many cancers either–about 10 percent of cancers limited to the prostate and 2 percent of those that had spread outside the gland. It also picked out 78 percent of the cancers in men who had normal PSA results but nonetheless had prostate cancer.

"It's certainly interesting, and it seems to be promising in those men whose PSA is in midrange," says Howard Scher, chief of the genitourinary oncology service at the Sidney Kimmel Center for Prostate and Urologic Cancers at Memorial Sloan-Kettering Cancer Center in New York. But the test needs to be validated in men of different age groups, among much larger populations, and in different labs, he says. And this test, like the PSA, can't identify which cancers are likely to grow slowly and cause no harm and which need aggressive treatment. "That's the holy grail in my mind," says Getzenberg (who has financial ties to the test's manufacturer, Onconome Inc.).

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