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 olderthe age group most
susceptible to prostate cancerfrom 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 patients
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
patients 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
This research combined a unique resourceDIANONs
large, proprietary database of clinical caseswith 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.