A new urine test can tell prostate cancer from an enlarged prostate -- but can't tell whether the cancer is deadly.
The test, from San Diego-based Gen-Probe, is approved in some European countries but not in the U.S. It detects genetic material -- RNA -- from prostate cancer gene 3 or PCA3.
PCA3 (previously known as the DD3 gene) is found only in the prostate. When prostate cells become cancerous, their PCA3 genes go wild. Prostate cancer cells express 60 to 100 times more PCA3 RNA than normal cells.
That means the PCA3 test can do things the current PSA test can't do. The PSA test detects prostate-specific antigen, a protein given off by all prostate cells. If a man has an enlarged prostate -- a noncancerous condition called benign prostatic hyperplasia or BPH -- his PSA level can go up. This often triggers unnecessary biopsies and, sometimes, unnecessary surgery.
"The beauty of this test is it seems to be independent of the BPH component," Mark Emberton, MD, of the Institute of Urology at University College London, tells WebMD. "But it is not a perfect test. It does not rule out -- or rule in -- clinically meaningful disease."
Emberton, who has no financial links to Gen-Probe, reported several studies of the PCA3 test at last week's annual meeting of the British Association of Urological Surgeons in London.
The studies showed that the PCA3 test isn't influenced by the size of the prostate, even in people with BPH. And they showed that the test can help men decide whether they need a repeat prostate biopsy. Prostate biopsy involves multiple needle punctures into the walnut-sized prostate gland.
"This test is going to be of value in two currently problematic areas," Emberton tells WebMD. "It will help men with a [relatively] low PSA who need reassurance but don't want an invasive test. And it will help men with a negative biopsy but a rising PSA decide whether they need a second set of biopsies."
Learning How to Use the Tests
The PCA3 gene was discovered by Marion Bussemakers, PhD, while she was working in the laboratory of William B. Isaacs, PhD, professor of urology and oncology at Johns Hopkins Brady Urological Institute. Isaacs is among the patent holders for the diagnostic use of the PCA3 gene.
"I am very excited by these new findings," Isaacs tells WebMD. "There is no question we need better ways to find who has prostate cancer and who needs to be treated. … [PCA3] is among the most prostate-cancer-specific markers ever identified."
If the PCA3 test is so good at detecting prostate cancer, will it replace PSA tests and prostate biopsies? No, Isaacs and Emberton say. That's because if a man lives long enough, he's very likely to develop prostate cancer.
Emberton says 80 percent of 80-year-old men and at least 50 percent of men over 50 have prostate cancer. Yet no more than 2 percent of men with prostate cancer die of the disease. Men who learn they have prostate cancer still face a question that science can't fully answer: When is their prostate cancer deadly and when is it something they can live with?
"This test will not help us find who needs treatment," Emberton says. "It just tells us prostate cancer is likely to be present -- nothing about the nature of the cancer."
Isaacs notes that 20 years after its introduction, doctors still are learning how to use the PSA test. He suggests that it will take time to learn how best to use the PCA3 test, too.
"Yes, prostate cancer is extremely common. You can argue there is overtreatment," he says. "On the other hand, there are still 28,000 U.S. men dying each year of prostate cancer -- and we certainly aren't overtreating those guys. So we need to know which cancers need to be treated. I hope the PCA3 test will be helpful for that."
By Daniel J. DeNoon, reviewed by Louise Chang, MD
SOURCES: British Association of Urological Surgeons, London, Nov. 23-24, 2006. News release, Gen-Probe. Mark Emberton, MD, Institute of Urology, University College London. William B. Isaacs, PhD, professor of urology and oncology, Johns Hopkins Brady Urological Institute, Baltimore.