Wednesday, September 21, 2005
A new blood test for prostate cancer is a “promising technique,” write the test’s inventors in The New England Journal of Medicine.
The test just requires a routine blood draw. But it isn’t ready for use yet, note Arul Chinnaiyan, MD, PhD, and colleagues.
If successful in other studies, the new test could enhance and perhaps eventually replace PSA blood tests, states Chinnaiyan, in a news release.
PSA (prostate specific antigen) is made by the prostate. High PSA levels can indicate prostate cancer. But they can also signal noncancerous conditions, such as an enlarged prostate, which limits the use of this test as a method of screening for prostate cancer.
“Initially, we envision this new test could be used as a supplement to PSA,” states Chinnaiyan, a pathology professor at the University of Michigan.
“A physician might suggest a patient with an elevated PSA have this test before a biopsy to better determine whether it’s a cancerous or benign condition. In the future, I think this could replace PSA,” he continues.
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Many men who get biopsies after PSA tests turn out not to have prostate cancer.
Reliance on PSA for the detection of early prostate cancer is still unsatisfactory, especially because many times (around 80 percent of the time) elevated levels of the protein (PSA) turn out not to be from prostate cancer, write the authors.
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Building a Better Test
First, Chinnaiyan’s team studied a large library of prostate cancer tissues. They found 22 proteins that they thought would make a good prostate cancer blood test. Researchers have found that patients with cancer produce antibodies against proteins found on tumors.
Next, they looked for those antibodies in blood from men with and without prostate cancer.
All of the prostate cancer patients had had biopsies showing localized prostate cancer. That means their cancer hadn’t spread beyond the prostate. The patients were also at least 40 years old and hadn’t had prostate cancer therapy before.
The new blood test usually worked in detecting only those men who had prostate cancer, the study shows. But two out of 70 healthy men and seven out of 69 men with prostate cancer were misclassified.
Finally, the scientists tested 128 more blood samples, 60 of which came from prostate cancer patients.
Once again, the test’s results were mainly right. The test accurately identified prostate cancer 81 percent of the time and correctly showed no cancer 88 percent of the time, the researchers report.
It’s not yet known if the test will work in men with other prostate conditions, autoimmune system problems, or other diseases, write the researchers.
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By Miranda Hitti, reviewed by Brunilda Nazario, MD
SOURCES: Wang, X. The New England Journal of Medicine, Sept. 22, 2005; vol 353: pp 1224-1235. News release, University of Michigan.