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EPCA-2: A Highly Specific Serum Marker for Prostate Cancer
(May 2007)
Drs. Robert Getzenberg,
Alan Partin et al., working at the University of Pittsburgh and Johns
Hopkins University, in this article describe the early developmental
studies suggesting greater specificity of a new biomarker, EPCA-2 (Early
Prostate Cancer Antigen-2) as compared to the
standard PSA for detection of "overall prostate cancer." Their new test
also was "highly specific in discriminating between people with and
without prostate cancer." An additional assay attribute permitted
"differentiating between localized and extracapsular disease." EPCA-2,
an epitope residing in "nuclear structural elements of prostate cancer
cells", is measurable in serum, and the initial studies used a cutoff
set at 30 ng/mL.
The test was validated
by analyzing EPCA-2 levels in six categories of people - all told 330
individuals: a collection of men with and without cancer whose PSA
values were less than 2.5 ng/mL; men with localized or non-organ
confined disease, or BPH; and a diverse group of controls. In 98 men
with no evidence of cancer or a negative prostate biopsy whose PSA
levels were <2.5 ng/mL, and in 35 men with BPH, the specificity of the
new test was 92% vs. 65% for PSA. Its sensitivity was 94% in 80 men with
local or non-organ confined cancer.
The assay for EPCA was
"highly accurate in separating men with organ confined disease from
those with non-organ confined disease" as determined by receiver
operator characteristic curves. Additionally, the study included
evaluation of pre- and post-prostatectomy assays in ten men. The
initially elevated PSA and EPCA-2 values in these men fell in tandem,
with all PSA values dropping to <0.1 ng/nL; and their elevated EPCA-2
values also showed a matching drop to comparably low values. The assay
is being further refined to lower the background test noise so as to
yield a result that more selectively reflects prostate cancer. In an
interview (Health Day News) Dr. Getzenberg was quoted as summarizing the
performance of the test by saying "a specific level of EPCA-2 identified
90 percent of men with cancer confined to the prostate and 98 percent of
those in whom it had spread beyond the gland. The test was negative in
97 percent of men without prostate cancer."
It
is premature to consider the use of this test in screening studies.
Considerable further validation is in order. But there is promise that
the EPCA-2 test will offer advantages superior to our historic PSA test.
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