Prostate cancer test’s accuracy cited
A new prostate test that relies on measuring levels of a blood protein called EPCA-2 accurately found cancer 94% of the time, a significant improvement over the current PSA test, according to a study released Wednesday.
Each year, about 1.6 million men undergo biopsies because they test positive on a PSA test -- but only about 230,000 of them actually have cancer.
The new test for EPCA-2 -- or early prostate cancer antigen -- not only detected prostate cancer but also determined whether it had spread to other parts of the body, according to the study published in the journal Urology.
“It could allow us to help patients decide if they need a biopsy or if it’s tame or has the ability to invade outside the prostate,” said Robert H. Getzenberg, director of research at the James Buchanan Brady Urological Institute at Johns Hopkins University in Baltimore and a coauthor of the study.
The test still faces large-scale clinical trials and review by the Food and Drug Administration, but it could be available in early 2008, said Getzenberg, who is a consultant to Seattle-based Onconome Inc., which is developing the test technology.
Prostate cancer is the second leading cause of cancer death in men after lung cancer, according to the American Cancer Society. About 27,000 die from prostate cancer a year, the society said.
Rectal examination and the PSA -- or prostate specific antigen -- test, which was approved in 1994, have been the primary methods of detecting the cancer.
But questions about the accuracy of the PSA test have been building. It has a high level of false positives and misses about 15% of prostate cancers.
Many false positive results require patients to undergo a biopsy, an unpleasant surgical procedure where prostate samples are taken for analysis.
Another problem is that the PSA test does not distinguish between the cancer’s aggressive form, which is frequently fatal, and a slow-growing form that patients can safely live with.
“The PSA is a flawed marker. Everybody agrees with that,” said Dr. Laurence Klotz, chief of urology at Sunnybrook Health Sciences Center in Toronto. “The search for a better marker is intense.”
In hunting down a new marker, Getzenberg said his team found that the EPCA-2 protein was structurally different in cancerous and normal prostate cells.
The researchers measured the EPCA-2 levels in the blood of 385 men who were known have cancer or were free of it.
Men who had an elevated EPCA-2 test indeed had cancer 94% of the time, compared with only about 19% of men with an elevated PSA result, reported in previous studies. The test falsely sounded an alarm 3% of the time, according to the report.
The EPCA-2 test missed about 6% of existing cancers. The PSA test misses about 15% of existing cancers, according to previous studies.
“It’s pretty exciting,” said Dr. Mark Scholz, a Marina del Rey oncologist specializing in prostate cancer. “PSA testing has led to over-treatment. With a more accurate test like this, one of the big pluses right away would be fewer biopsies.”
But Scholz said the PSA still has value. “If you do two tests, you have a greater likelihood of finding the truth,” he said.
Other prostate tests are in the pipeline, including a urine-based genetic test and another blood test.