Free PSA Test Separates Benign From Malignant Prostate
The free PSA (fPSA) test is significantly better at distinguishing prostate
cancer from benign prostatic conditions than more traditional follow-up
methods used to improve PSA testing, according to a major new study to be
published in the August issue of Urology.
The Hybritech(r) free PSA test, manufactured by Beckman Coulter, Inc., was
used in the study. Hybritech free PSA is the only fPSA assay approved by the
Food and Drug Administration (FDA) for clinical use to aid in distinguishing
prostate cancer from benign prostate conditions.
The study compared fPSA results with the commonly used approaches of
age-specific PSA reference ranges and PSA density calculations in men aged
50 years and older with total PSA results between 4 ng/mL and 10 ng/mL and
who had negative digital rectal examinations.
"PSA is the best cancer tumor marker in all of medicine, but there is
understandable pressure to improve its accuracy. This study shows that free
PSA is the best available way to improve the accuracy of total PSA tests,"
said lead author of the study William J. Catalona, M.D., of the Division of
Urologic Surgery at Washington University School of Medicine.
The PSA test is limited by its relative lack of accuracy in men whose PSA
levels fall in the so-called "diagnostic gray zone" of 4 to 10 ng/mL.
Three-quarters of the men in this range do not have cancer.
Prior to the development of the fPSA test, men in this group were routinely
recommended for a prostate biopsy, which can be both painful and costly.
Physicians who use age-specific reference ranges as a follow-up to PSA
testing will factor in a patient's age relative to his PSA value, while the
PSA density method requires the physician to perform a costly ultrasound to
calculate serum PSA levels divided by the prostate volume.
In contrast, because fPSA assays -- which measure the amount of unbound or
"free" portion of prostate-specific antigen -- do not require an
accompanying ultrasound, they are more cost-effective than PSA density
In the new study, 773 men ages 50 through 75 had a palpably benign prostate,
total PSA levels between 4 and 10 ng/mL, a negative digital rectal
examination and a histologically-confirmed diagnosis.
With these patients, follow-up tests were conducted using the Hybritech free
PSA assay, PSA density tests and age-specific reference range cutoffs to
increase the accuracy of PSA testing for prostate cancer detection and for
staging the severity of the disease.
While all three methods increased the accuracy of total PSA testing in
distinguishing benign prostatic conditions from prostate cancer,
age-specific PSA cutoffs were less sensitive than fPSA and missed 20 percent
to 60 percent of all cancers in men over 60 years of age.
In addition, the fPSA ratio and PSA density tests both had a 95 percent
cancer detection rate when the fPSA ratio of 25 percent and a PSA density
level of 0.078 were used. The study also found both methods equally
effective at predicting cancer aggressiveness.
The results of the study suggest that fPSA assays can be safely used as an
alternative to PSA density tests -- which require ultrasounds -- as a less
invasive, less costly option to increase the accuracy of PSA tests.
Prostatic biopsy is required for actual diagnosis of prostate cancer.
"Results of this study are significant because they show that free PSA tests
can improve the accuracy of PSA tests and are more sensitive than
age-specific reference ranges," Dr. Catalona said. "They are as accurate as
PSA density tests in the study, but less costly. Other studies have also
shown that free PSA ratios can provide the bonus of telling patients and
physicians how aggressive the cancer is."
The study was supported by a research grant from a subsidiary of Beckman
Beckman Coulter, headquartered in Fullerton, Calif., is a leading provider
of instrument systems and complementary products that simplify and automate
processes in life science and clinical laboratories. The company's products
are used throughout the world in all phases of the battle against disease,
from pioneering medical research and drug discovery to diagnostic testing
that aids in patient treatment.
02-Aug-2000 Reprinted from the www.unisci.com archives, with the permission of
UniScience News Net, Inc.