Testing further for a form of prostate-specific
antigen (PSA) can help urologists find, stage, and classify prostate
cancer in men whose PSA tests are ambiguous, according to a
multicenter study that included The Johns Hopkins Hospital. The
additional test, which is routinely available for all men taking the
PSA test, can also help patients and their doctors determine the best
course of treatment. The test measures free PSA, the form of PSA not
bound to proteins in the blood. According to the study, the higher
the percentage of free PSA compared to the bound form, the smaller
the tumor is likely to be, the less chance there is that it has
spread from the prostate, and the less likely it is that the disease
is the most aggressive form.
The study was reported in the October 1999 issue of The Journal of Urology.
At least one-third of localized cancers are understaged. The current
staging technique combines PSA tests with digital rectal
examinations, transrectal ultrasound, and biopsy Gleason grades. The
most popular assessment of whether the tumor has spread beyond the
prostate involves a nomogram that measures PSA, clinical staging, and
Gleason score. Earlier studies showed that a small percentage of free
PSA in the blood is associated with the more aggressive forms of
The study, involving seven medical centers, looked at 379 men with
prostate cancer and 394 with benign prostatic disease. The men all
fit into a gray diagnostic area: they had negative digital rectal
examinations but their PSA level was between 4.0 and 10.0 ng/mL and
75% had negative biopsies.
The men in the study ranged from 50 to 75 years of age (median age
was 62 years). The study found that a higher percentage of free PSA
was associated with more favorable histopathologic findings. The
lower the percentage of free PSA, the larger and more advanced the
tumor was likely to be, with a milestone set at 15%.
The researchers concluded that the percentage of free PSA could be
used for diagnosis and staging. Patients with more than 25% free PSA
probably did not need a biopsy unless they had a family history of
prostate cancer. Also, patients with more than 15% free PSA had the
most favorable outcomes. Using free PSA would detect 95% of cancers
and spare 20% of men with benign disease from having to undergo biopsies.
Beckman Coulter provided financial aid for the study.