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Prostate Cancer Could Be Discovered Earlier with New
Blood Test
Researchers discover protein signatures the may
improve early diagnosis
Sept. 23, 2005 - A new study shows that testing
blood samples for antibodies that target prostate cancer cells may help
identify patients with early stages of the disease, which primarily is
found in senior citizens. In the September 22, issue of New England
Journal of Medicine, researchers report the findings may lead to a new
test that could complement the prostate specific antigen (PSA) test in
detecting early stage prostate cancer.
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Previous studies have found that men with normal
blood levels of PSA (4.0 ng/ml or less) can have prostate cancer.
Furthermore, PSA-based prostate cancer screening has a high rate of
false-positive results (up to 80 percent). Therefore, scientists have
been looking for additional ways to adequately screen for early disease.
Using PSA testing alone results in millions of
dollars being spent on prostate biopsies due to false positive results.
We dont yet know if our new findings will save lives, but there could
be a major cost saving by decreasing the number of prostate biopsies
performed every year, said Sudhir Srivastava, Ph.D., Chief, Cancer
Biomarkers Research Program and Director for the EDRN.
The panel of 22 target proteins identified in this
study showed an 88.2 percent specificity value for prostate cancer,
which indicates the proportion of those tested who did not have cancer
and were correctly identified as being free of disease. The test also
showed an 81.6 percent sensitivity value, indicating the proportion of
those patients with cancer that were correctly diagnosed as having
prostate cancer.
Scientists know that cancer patients produce
antibodies to proteins, called antigens, which are present on the
surface of tumor cells. Antibodies themselves are proteins produced by
immune cells to help fight and destroy viruses, bacteria, and other
foreign substances that invade the body. As a cancer cell grows, normal
antigens can be presented on a cell surface in a different way. The body
then recognizes these antigens as foreign and produces antibodies to
them. These particular antibodies are termed autoantibodies, because
they react to a substance produced by the body itself.
"In this study, we took advantage of the body's own
immune system as a detector of prostate cancer, said Arul Chinnaiyan,
M.D., Ph.D., study leader, University of Michigan Medical School, Ann
Arbor. While the present study focused on the detection of prostate
cancer, this general approach has potential to be developed for other
cancers as well as for other human diseases that in some way perturb the
immune system."
The use of autoantibody signatures may be useful in
combination with PSA testing in reducing the number of false negative
and false positive tests obtained then when using PSA testing alone.
Statistical analysis of these results shows that the protein panel
performed better in distinguishing between prostate cancer patients and
controls than the PSA test. The panel of 22 proteins predicted the
presence of cancer accurately 92.7 percent of the time, while PSA
predicted the presence of cancer only 79.6 percent of the time. The use
of autoantibody signatures may be most informative in assessing the need
for a biopsy in patients with PSA values of 10ng/ml or less.
Identification of autoantibodies is an exciting
area of research. We are also looking to see if the autoantibodies
produced against prostate cancer cells are specific only to this
disease, said Srivastava. Knowledge of whether antibodies are specific
to particular organs will be important when considering a design for any
new test.
A total of 257 blood samples were tested for novel prostate cancer
autoantibodies; blood samples from 119 patients with prostate cancer
were studied prior to surgery and 138 samples were from patients without
prostate cancer. Among the 22 peptides found, the genes that code four
of them were identified: eIF4G1, BRD2, RPL13a, and RPL22.
Collaborators supported by the EDRN will further
analyze the peptide panel test. Both the reproducibility of this study
protocol and new blood samples will be used to validate the peptide
panel. For clinical application to occur, the test will need to be
validated in different populations and at various EDRN testing sites; a
process that is being planned.
The study was supported by the Early Detection
Research Network (EDRN), an initiative of the National Cancer Institute
(NCI), part of the National Institutes of Health. For more information
about NIH and its programs, visit
http://www.nih.gov.
For more information about cancer, visit the NCI
Web site at
http://www.cancer.gov or call NCI's Cancer Information Service at
1-800-4 CANCER (1-800-422-6237).
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