Researchers
Look for More Reliable Prostate Cancer Tests
A test that focuses on a blood protein produced by prostate
cancer cells may improve disease diagnosis, researchers report in the medical
journal Urology.
Levels of this protein, called prostate cancer antigen-2
(EPCA-2), appear to give a more accurate picture of cancer present in the body,
experts say.
"We've been able to show that blood levels of it are low
in normal individuals and high in prostate cancer, and that it distinguishes
between cancers that are confined to the prostate and those that have spread
outside the gland," explains study lead researcher Dr. Robert H. Getzenberg,
at Johns Hopkins University.
Prostate cancer is the most common cancer in American men.
There will be some 218,890 new cases in the US this year and 27,050 deaths
linked to the disease, the American Cancer Society (ACS) estimates.
Prostate cancer is highly curable if caught early, however.
In the new study, Dr. Getzenberg's team measured blood levels
of EPCA-2 in 330 men.
Some of the men had an enlarged but non-cancerous prostate
gland, some had prostate cancer but displayed normal PSA levels, some had prostate
cancer that had spread beyond the gland, and some had other cancers or medical
conditions.
A specific level of EPCA-2 identified 90 percent of the
men with cancer confined to the prostate and 98 percent of those in whom it
had spread outside the gland.
The test was negative in 97 percent of the men without prostate
cancer, the researchers say.
That is an improvement on the standard PSA test, which provides
only a rough guide in many such cases.
For example, a high blood level of PSA can sometimes indicate
prostate cancer, but often a biopsy reveals no such malignancy.
Conversely, a low PSA level does not necessarily mean that
a man is free of prostate cancer, note the study authors.
"If this test works out, we can avoid a lot of unnecessary
biopsies," says Dr. Getzenberg.
About 1.3 million men in the US will have
biopsies this year to find only 200,000 cancers, he notes. "Clearly, we need
further validation."
"We are doing good-sized validation studies, and we are
also testing the ability of the marker to identify aggressive forms of the
disease," explains Dr. Getzenberg.
Spotting especially life-threatening prostate
tumors is "the
holy grail" of diagnosis, he says. Current PSA testing cannot distinguish between
cancers that will grow so slowly that they pose no danger to life and those
that require quick action.
The hope is that the EPCA-2 test will identify
men whose slow-growing cancers make them candidates for "watchful waiting" rather
than immediate surgery or other treatment.
The Johns Hopkins team, working with researchers from the
University of Pittsburgh, has licensed the test to a company, Onconome Inc.
"We have already met with the Food
and Drug Administration [FDA] and understand the kind of trial we
need to do [for approval]," he says. That means that the test might be available
in the next 18 months, he says.
Dr. Durado Brooks, director of prostate and
colorectal cancers at the ACS, says EPCA-2 test looks promising.
Dr. Brooks adds that more work must be done.
"It does seem to have very high sensitivity and specificity
for prostate cancer," says Dr. Brooks. "The challenge is taking it out of this
isolated and rigorous setting and seeing how it performs in other laboratories
and also in much larger screening-type populations."
If the test does prove to be accurate in
larger populations, it could be "very useful" in prostate cancer diagnosis,
explains Dr. Brooks.
But the real hope that it could single out those cases requiring
immediate treatment from those that could be left for watchful waiting has
yet to be proved, he says.
Always consult your physician for more information.
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