A+PSA test gives better results in testing for prostate cancer
31 May 2011
A new test for prostate cancer that measures levels of
prostate specific antigen (PSA) as well as six specific antibodies found
in the blood of men with the disease was more sensitive and more
specific than the conventional PSA test used today, according to a study
by researchers at UCLA’s Jonsson Comprehensive Cancer Center.
The test, called the A+PSA assay, also reduced the rate of
false-positives, tests that indicate the presence of cancer when no
disease is actually present, said Gang Zeng, an associate professor
of urology, a Jonsson Cancer Center researcher and senior author of
“This is a very promising new approach,” Zeng said. “Instead of
using just one parameter, PSA, to test for prostate cancer, we use
multiple parameters that can be measured in a single reaction.”
The study appears in the May issue of the Journal of
The conventional PSA test for prostate cancer has been used for
nearly 30 years and is not specific enough in delineating between
malignancies and non-malignant diseases of the prostate, such as
benign prostatic hyperplasia (BPH), an enlarging of the prostate
common in aging men that increases PSA levels, Zeng said.
The retrospective study used blood taken before surgery from 131
patients from UCLA, Japan and France with biopsy-confirmed prostate
cancers and compared results to blood taken from 121 men with either
BPH or prostatitis, an infection or inflammation of the prostate
that increases PSA levels. The study focused on six specific
prostate-cancer associated antigens – NY-ESO-1, SSX-2,4, XAGE-lb,
AMACR, p90 and LEDGF - which are found predominantly in patients
with prostate cancer and not in benign prostate conditions.
The A+PSA assay looked simultaneously for PSA and antibodies to
the six prostate-cancer associated antigens in a single reaction
test done in a laboratory, much like PSA is measured. The new test
takes about two hours, again similar to the PSA test. The test
results in an index of numbers used to diagnose cancer, with a score
of 0 to 0.5 indicating a benign result and 0.5 to 1 indicating the
presence of prostate cancer, Zeng said.
In the new test, sensitivity - the percentage of men with
prostate cancer who were correctly identified as having a malignancy
- was 79 percent compared to the 52 percent found in PSA testing.
Specificity - the percentage of healthy men who were correctly
identified as not having prostate cancer - was 84 percent compared
to the 79 percent found when testing for PSA alone.
The rate of false-positives using conventional PSA testing is 21
percent. With the new A+PSA assay, the false-positive rate is 16
percent, Zeng said.
“Science has improved so much since the PSA test was developed
and I think it’s time for a more specific and sensitive test to be
developed,” Zeng said. “I think we have a test that has great
potential to improve the diagnosis of prostate cancer. I knew it
would be better than the classic PSA test, but I was amazed at how
much better it really was in this study.”
Dr. Allan Pantuck, an associate professor of urology, Jonsson
Cancer Center researcher and a study author, said a more specific
and sensitive test for prostate cancer would be a welcome addition
to the diagnostic tool box.
“While measuring PSA is useful in identifying men with prostate
cancer, some men with prostate cancer have a normal PSA level and
small elevations in PSA above normal may be produced both by
prostate cancer as well as an enlarged but benign prostate,” Pantuck
said. “Combining PSA with a panel of tests that measure an
individual man’s anti-cancer immune response may better identify who
has prostate cancer and who can be spared an unnecessary invasive
Zeng and his team are working now to adjust and improve the
statistical index used in their test to generate the “score.” He’d
like to do a prospective study that would include the racial, ethnic
and age information for each man who provides blood. The test could
perhaps be altered for men over a certain age if the antibody levels
found in their blood vary. African-American men may also have
varying levels of the six antibodies. There also are additional
antibodies that could be added to the assay that may improve both
the sensitivity and specificity of the test, Zeng said.
“Different men may have different levels of the six antibodies or
different antibodies all together based on their race, age and
ethnicity,” Zeng said. “We want as accurate an assay as we can
Any new prostate cancer test would have to be approved by the US