An experimental blood test detects prostate cancer so accurately that it may supplant prostate-specific antigen (PSA) levels as a screening tool.

Researchers at Johns Hopkins University in Baltimore discovered an early prostate cancer antigen (EPCA-2) that functions as a biomarker. In a sample of 330 men, EPCA-2 levels were positive in 94% of those who had prostate cancer and negative in 97% of those who didn’t. The test also differentiated between cancers that were confined to the prostate and those that had spread.

Current screening protocols for prostate cancer rely on elevated levels of PSA. Men whose PSA is >2.5 ng/mL are considered at risk, and a biopsy is required for confirmation. About 1.6 million biopsies are done each year, but four of five have negative results, says Robert H. Getzenberg, PhD, director of urologic research at Johns Hopkins and the lead investigator. PSA tests also generate a number of false positives and miss some cancers altogether. The EPCA-2 test identified 78% of men who had prostate cancer with PSA levels <2.5 (Urology. 2007;69:714-720).

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Three quarters of the benign prostatic hypertrophy (BPH) patients in the study had an EPCA-2 below the diagnostic level of 30. Getzenberg says this is significant because BPH is often associated with elevated PSA levels, leading to misdiagnosis. “A blood test based on EPCA-2 may greatly improve our ability to accurately detect prostate cancer early and minimize the number of false positives, therefore lowering the number of unnecessary biopsies,” Dr. Getzenberg says.

The researchers found levels of EPCA-2 were highest in men whose cancer had spread beyond the prostate, making it much easier to detect advanced disease than with PSA tests. “This is important, since cancer that has spread is more deadly, which makes a tool that detects it early even more crucial,” says Dr. Getzenberg. He’s planning a larger clinical trial and estimates that the test could be approved within 18 months.

The study was funded by the National Cancer Institute and Onconome, Inc., a biotechnology firm in Seattle. Dr. Getzenberg, who holds a patent for the test, works for Onconome as a paid consultant and will receive royalties if the test is marketed.