SEATTLE--A study of 1,695 cancer-free men found that PSA density
provides a far more accurate screening assay for detection of
prostate cancer than PSA serum concentration, Robert Kane, MD,
of Harvard Medical School, said at the Pacific Northwest Cancer
Foundation Meeting on Transperineal Brachytherapy for Early Stage
PSA density is calculated by relating the serum PSA concentration
(ng/mL) to the volume of the prostate gland in a particular patient.
Serum PSA testing is very useful for following patients with known
prostate cancer, to assess the effectiveness of therapy and the
progression of the cancer, Dr. Kane said. But for prostate cancer
surveillance, the considerable number of false-positives in men
who simply have enlarged glands results in emotional cost to the
patient and substantial economic cost to the health-care system.
Lacks Specificity in Both Directions
The serum PSA test also lacks specificity in the other direction.
Dr. Kane reported that in several studies, 23% to 43% of patients
with organ-confined prostate cancer had normal PSA values.
The multicenter study, conducted by Dr. Kane and other investigators
as part of the American Cancer Society National Prostate Cancer
Detection project (Cancer, March 1, 1992), analyzed the distributions
of PSA concentrations in cancer-free men overall and also according
to differing prostate gland volumes, patient age, and the presence
or absence of symptoms of benign prostatic hypertrophy (BPH).
They found that neither age nor symptoms of BPH appeared to have
any effect on PSA levels when adjusted for gland volume. They
concluded that estimating PSA density (based on ng/mL/cc gland
volume) rather than relying on absolute serum levels may make
it possible to reduce the number of false-positive PSA results
in the general population.