imPSA superior to total PSA in distinguishing prostate cancer

Key Points

"The pilot results are accurate," said Mesut Remzi, MD, staff physician in the urology department, Medical University of Vienna, Austria. "In this cohort, serum total PSA is not an indicator for prostate cancer, but imPSA is. The next step is commercial development."

Comparing specificity

Conventional serum total PSA screening offers a specificity of about 40% for prostate cancer, Dr. Remzi reminded the moderated poster session, noting that research teams around the world are working on a variety of prognostic and diagnostic markers for prostate cancer, including different forms of PSA.

The latest study from Dr. Herwig's group compared the results of conventional screening using serum total PSA concentration to imPSA screening. The study population included 38 men with prostate cancer and 36 controls. The prostate cancer group included 18 men with localized disease and 20 men with metastatic disease. The control group included 20 healthy men and 16 men with BPH.

Members of the patient and control groups were recruited from the Medical University of Vienna and the Atrium Medical Center, Heerlen, the Netherlands. The men in both the patient and control groups had a mean PSA of 19.0 ng/mL and were similar in all other characteristics except for the presence of prostate cancer.

Researchers took peripheral whole blood samples from each of the men and isolated mononuclear cells. The isolated macrophages were analyzed for CD14+ and CD16+ using flow cytometry. Cells also were stained with a monoclonal antibody to PSA. Results were calculated in terms of the percentage of imPSA.

No statistically significant differences were seen between imPSA levels found within each of the three types of disease studied: BPH, localized prostate cancer, and metastatic prostate cancer.

BPH, cancer differentiated

Controls had a mean imPSA of 1.82, men with BPH had a mean imPSA of 2.95, men with prostate cancer had a mean imPSA of 12.76, and men with metastatic prostate cancer had a mean imPSA of 29.44. The p-value for prostate cancer identification was .001 and for met-astatic prostate cancer, .0001. Regression analysis established imPSA as an independent marker in both BPH and localized prostate cancer.

The consistency of imPSA levels recorded for each disease type stands in sharp contrast to the respective serum total PSA concentrations, which showed such high standard deviations that no distinction could be made between BPH and prostate cancer.

In this population, patients with BPH had a higher mean serum PSA, 19.28 ng/mL, than did patients with localized prostate cancer, 11.23 ng/mL. Only in men with metastatic prostate cancer did the mean serum PSA level of 203.2 ng/mL reach statistical significance (p=.001).

"We need new markers to differentiate between prostate cancer and benign conditions," Dr. Remzi said. "imPSA appears to meet that need. There is a significant difference between healthy controls, BPH, and prostate cancer, both localized and metastatic. This is seen to be a correlation with tumor volume, as well."