New PSA Test can Differentiate Benign From Malignant Disease

From The American Urological Association

ATLANTA—Austrian investigators report that they have devised a better method of testing for prostate-specific antigen (PSA) that may be more sensitive and specific than the currently used tests. The new technique, which measures the amount of intracellular PSA in peripheral blood macrophages, appears to be able to clearly distinguish benign disease from malignant disease.

New data presented at the 2006 annual meeting of the American Urological Association also indicate that this new PSA test is much more accurate in differentiating metastatic disease from localized prostate cancer.

The test was evaluated in a study that included 25 patients with prostate cancer and 10 healthy controls who underwent extracellular staining for CD14 and CD16 cells. First, flow cytometry (FACS Calibur, USA) was used to analyze cells according to extracellular signal for CD14^† and CD16^† (a marker for immune cell activation). Intracellular staining (to detect PSA) was then performed using a cell permeabilization kit and monoclonal antibodies against PSA (Clone ER-PR8). All the data were calculated as mean percentages with standard deviation of positive cells.

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“The current PSA test is a good marker for detecting prostate cancer, but the specificity is very low, so there is an urgent need for new markers. More than 70% of patients are undergoing biopsies because of high PSA levels, and they don’t have a cancer,” lead investigator Ralf Herwig, MD, assistant professor of urology, Medical University of Vienna, Austria, told .

“You can distinguish very well between benign prostatic hyperplasia, prostatitis, and localized and metastatic disease with this approach,” Dr Herwig said.

Results showed a mean percentage of PSA-containing macrophages of 0.58% in healthy controls compared with 14.75% in patients with localized prostate cancer and 84.67% in those with metastatic disease. With traditional measures of serum total PSA levels, the standard deviation was so high that the controls could not be distinguished from the other 2 groups.

The new test should be commercially available for use in primary care within the next 12 to 18 months.