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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In addition to an annual physical examination that includes blood, urine, and possibly other laboratory tests, the National Cancer Institute (NCI) and
the American Cancer Society (ACS) suggest
consulting your physician about these recommendations
for the evaluation of the prostate gland:
DRE (digital rectal examinations)
As recommended by your physician, DREs are usually conducted annually for men over the age of 50.
Men in high-risk groups, such as African Americans, or those with a strong family history of prostate cancer, should consult their physicians about being tested at a younger age.
PSA (prostate-specific antigen)
PSA is a blood test that measures the level of prostate specific antigen. PSA is a substance produced by the prostate gland, which may be found in higher amounts in men who have prostate cancer.
As recommended by your physician, the PSA test is usually done annually for men over the age of 50. Men in high-risk groups, such as African Americans, or those with a strong family history of prostate cancer, should consult their physicians about being tested at a younger age or more often.
If the DRE or PSA are unusual, your physician may repeat the tests or request an ultrasound and other procedures. These evaluation tools may include:
transrectal ultrasound (TRUS)
A test using sound wave echoes to create an image of the prostate gland to visually inspect for abnormal conditions such as gland enlargement, nodules, penetration of tumor through capsule of the gland, and/or invasion of seminal vesicles; may also be used for guidance of needle biopsies of the prostate gland and/or guiding nitrogen probes in cryosurgery.
computed tomography scan (Also called a CT or CAT scan.)
A diagnostic imaging procedure that uses a combination
of x-rays and computer technology to produce cross-sectional
images (often called slices), both horizontally and
vertically, of the body. A CT scan shows detailed images
of any part of the body, including the bones, muscles,
fat, and organs. CT scans are more detailed than standard
x-rays.
magnetic resonance imaging (MRI)
A diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
radionuclide bone scan
A nuclear imaging method that helps to show whether the cancer has spread from the prostate gland to the bones. The procedure involves an injection of radioactive material that helps to locate diseased bone cells throughout the entire body, suggesting possible metastatic cancer.
(lymph node and/or prostate) biopsy
A procedure in which tissue samples are removed (with a needle or during surgery) from the body for examination under a microscope; to determine if cancer or other abnormal cells are present.
The diagnosis of cancer is confirmed only by a biopsy.
Always consult your physician for more information.
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