Test shows promise in detecting prostate cancer

Researchers at the Johns Hopkins University School of Medicine are trying to develop a more reliable way to find prostate cancer. While experts say the new test is promising, they say it's too soon to know whether it really works better than older screening methods.

Experts note that the most commonly used screening test today — the PSA, which measures a protein called prostate-specific antigen in the blood — is far from perfect. The PSA doesn't find all cancers. It causes about 1.6 million American men to have needle biopsies each year, 80% of which are negative, says Robert Getzenberg, a Johns Hopkins professor. The American Cancer Society estimated that nearly 219,000 men will be diagnosed with prostate cancer this year and more than 27,000 will die from it.
That's why Getzenberg and other scientists are trying to improve cancer screening by searching for biomarkers — proteins in blood or urine that signal the presence of cancer. One potential new marker is early prostate cancer antigen, or EPCA-2. In a study released today from the April issue of Urology, Getzenberg says doctors may one day use this test to help men with high PSA results avoid unnecessary biopsies.

Using blood samples from 385 people, Getzenberg found that EPCA-2 correctly spotted 94% of prostate cancers. Previous studies have found that the PSA finds only about 80% of cancers. Just as important, he says, the new test produced false alarms in only 3% of patients. The new test was better than the PSA at helping to spot more advanced cancers. The EPCA-2 was 89% accurate in differentiating cancers inside the prostate gland from those that have spread beyond it; the PSA was 63% accurate.

Getzenberg notes that his results are still preliminary. He's collaborating with scientists at other universities to see if these results hold up over time. Scientists have yet to validate any of the dozens of potential new biomarkers found in recent years.

Ian Thompson, chairman of urology at the University of Texas Health Science Center in San Antonio, says he doubts the new test will replace the PSA. Instead, doctors likely will incorporate new biomarkers into a panel of tests that will help men gauge their risk of prostate cancer, says Thompson, who was not involved in the study.

Howard Parnes of the National Cancer Institute, who also was not involved in the Johns Hopkins study, notes that prostate screenings have not yet been shown to save lives. Finding more cancers could actually lead to "overdiagnosis" and "overtreatment," in which men are treated for slow-growing tumors that don't really need to be found. An ideal screening test, he says, would call attention only to lethal cancers.

Johns Hopkins and the University of Pittsburgh own the patent to the EPCA-2 test. They have licensed the test to Seattle-based Onconome Inc. Getzenberg, who has served as a consultant to Onconome, also is entitled to royalties from sales of the test, if it is approved. The study was financed by the NCI and Onconome.