NEW YORK--A new testing kit that measures free PSA (F-PSA), developed
by a French pharmaceutical firm, may improve the positive predictive
value (PPV) of PSA testing.
Because of the difficulty in distinguishing between prostate malignancies
and benign prostatic hypertrophy (BPH) with PSA levels of 4 to
10 ng/mL, the specificity of PSA testing is currently limited.
At the International Conference on Human Tumor Markers, Nathalie
Bedeau, of CIS bio international (Gif-sur-Yvette), described a
new assay that measures the ratio of total PSA to F-PSA.
Ms. Bedeau explained that PSA assays currently in use measure
total PSA without making a distinction between F-PSA and PSA bound
to alpha-1-antichymo-trypsin. It is known that the proportion
of F-PSA is higher in patients with BPH than in those with prostate
cancer. The ability to measure both total PSA and F-PSA, and to
derive a ratio between the two, has been shown to nearly double
the positive predictive value of PSA testing.
A first trial of 105 patients with prostate pathology (prostate
cancer or BPH) showed that total PSA (with a cut-off of 4 ng/mL)
yielded a PPV of only 48%. In the same population, the use of
F-PSA measurement and the ratio of F-PSA to total PSA yielded
a PPV of 87%.
The CIS bio international kit is available in Europe, and it holds
promise as a way to improve the specificity of PSA testing as
a diagnostic tool, Ms. Bedeau commented.
[Editors' note: In the US, Hybritech has developed a similar assay,
to be tested in a large clinical trial coordinated by Washington
University of St. Louis.]