Use of Percent-Free PSA Improves Diagnosis of Prostate Cancer, Studies Show

Determination of the percentage of free prostate specific antigen (PSA) via a simple blood test improves the diagnosis of prostate cancer and may limit the need for biopsies, according to two studies published in the September issue of Urology. In particular, the new test developed by DIANON Systems, (Stratford, Connecticut) helps differentiate benign prostatic hyperplasia (BPH) from prostate cancer among men with moderately elevated PSA levels.

Currently, measurement of PSA levels in blood is the most clinically useful test for the early detection of prostate cancer. The National Cancer Institute (NCI) noted that physicians increased their use of the PSA test for men age 65 and older—the age group most susceptible to prostate cancer—from 1,430 tests per 100,000 men in 1988 to 18,000 per 100,000 men in 1991.

The protein is not specific for cancer, and higher levels can be found among men with BPH, however. Physicians must rely on additional tests, including invasive prostate needle biopsies, to diagnose prostate cancer and benign prostate disease. Percent-free PSA is a new test designed as a supplemental test for men with moderately elevated total PSA levels.

Age, Total PSA, and Percent-Free PSA

By analyzing more than 4,000 men, researchers from DIANON Systems and Alan W. Partin, MD, PhD, associate professor of urology at The Johns Hopkins School of Medicine, and physician at Hopkins’ Brady Urological Institute, demonstrated that considering a patient’s age and total PSA levels when interpreting percent-free PSA is more effective than any of the variables independently.

The study also described the development, validation, and accuracy of a statistical model combining age, total PSA, and percent-free PSA to calculate the risk of prostate cancer. These risks can be used to counsel patients regarding the need for a biopsy and are 48% better than percent-free PSA alone in identifying men who do not need a prostate needle biopsy.

Distinguishing Prostate Cancer from BPH

The second DIANON study, the largest to examine the performance of percent-free PSA in men with low PSA values, determined that percent-free PSA was best used as a supplemental test to distinguish between prostate cancer and benign prostate disease when the patient’s total PSA level was at least 4.0 ng/mL.

Researchers from DIANON Systems, along with Stacy J. Childs, MD, FACS, associate clinical professor of urology at the University of Colorado Health Sciences Center, examined the performance of percent-free PSA in 479 men whose PSA values were less than the established normal limit of 4.0 ng/mL. The study concluded that percent-free PSA was not an indicator of prostate cancer until total PSA reached 4.0 ng/mL and that the percent-free PSA test should be used only in men with a PSA level ³ 4.0 ng/mL.

“This research combined a unique resource—DIANON’s large, proprietary database of clinical cases—with the expertise of our researchers and collaborators to demonstrate more reliable and effective uses for a new technology,” said Kevin Johnson, president and CEO of DIANON.