The Search for More Accurate Prostate Cancer Tests
April 2, 2000 (San Francisco) -- Prostate cancer strikes about 180,000 American men each year and every year it kills 37,000 men. All of those deaths are preventable if the cancer is detected early, and cancer experts meeting here are struggling to find a test that will provide that early answer.
Currently the best test for prostate cancer is a blood test that checks for levels of prostate-specific antigen, called PSA. When prostate cancer is present, the concentration of PSA in the blood goes up. But cancer isn?t the only thing that drives up PSA. A non-cancerous condition called benign prostatic hyperplasia or BPH -- actually just an overgrowth of tissue in the normally walnut-sized gland -- also sends PSA levels soaring. So cancer researchers have been searching for either a different test or a way to make PSA testing more reliable.
Peter H. Gann, MD, ScD, says one way to make PSA testing better would be to test for what is called free PSA. Standard tests give a total PSA level; meaning that some of the antigen is "bound" to other molecules and some is just circulating freely in the blood. Gann tells WebMD that free PSA actually decreases when prostate cancer is present but is unaffected by the presence of BPH. Gann is associate professor of preventive medicine at Northwestern University School of Medicine in Chicago.
If one tests for both total PSA and free PSA, the result is a test that is more accurate, he says. What happens is that fewer cancers are actually detected but also there are many fewer false positives. Men who have a positive PSA test often undergo a surgical biopsy, which many times is negative, says Gann.
He says that most of the cancers missed by free PSA don?t appear for "nine years or later." He says that the long time period would provide "many opportunities to identify these missed cases." The bottom line, says Gann, is there would be a substantial reduction in unnecessary biopsies, saving both money and emotional strain. Moreover, he says that adding free PSA to the standard test "doesn?t add any additional cost."
Gann discussed his paper at the American Association for Cancer Research meeting. The conference also featured a study of an experimental urine test for prostate cancer. This test screens for the presence of a genetic mutation. This defect is found in more than 90% of prostate cancers but is not present in normal tissue or in tissue taken from men with BPH.
Paul Cairns, PhD, a researcher at Fox Chase Cancer Center in Philadelphia, tested urine samples and tissue from 28 men who had curable prostate cancers. They found the mutation in tissue taken from 22 of the men and identified it in the urine from six of those 22, Cairns tells WebMD. He says he is investigating urine because the "prostate surrounds the urethra and it is very likely that some of these cancerous cells would spill into the urine."