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Jan. 31, 2002 |
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Value of PSA for diagnosing prostate cancer questioned PALO ALTO, Calif. -- Jan. 31, 2002 (Cancer Digest) -- A widely used blood test for prostate cancer is clinically unreliable according to Stanford University Medical Center researchers. The new study led by Dr. Thomas Stamey, professor of urology at Stanford found that prostate specific antigen (PSA), a marker frequently used by doctors as an indicator of prostate cancer risk, is not meaningfully linked to prostate cancer, rather a rise in PSA results from harmless increases in prostate size, commonly known as benign prostatic hyperplasia or BPH. "For any level of serum PSA - from 2 to 9 nanograms per milliliter - there is no way you can turn to a patient and say you've got prostate cancer," said Stamey in the January issue of The Journal of Urology. Levels of PSA, a normal product of the prostate gland, have been thought to increase in men with early prostate cancer. Men aged 50 or older whose PSA levels exceed a certain cutoff are monitored and may undergo prostate biopsy as standard procedure. But biopsies cannot distinguish between cancers that should be of concern and "small cancers that will never bother a patient if they live to the age of Methuselah," Stamey said. In order to address the relationship between PSA and prostate cancer risk, Stamey and his colleagues examined 875 prostates that had been surgically removed from cancer patients at Stanford University Medical Center between December 1984 and January 1997. The researchers measured the volume of cancer in each of the prostates, as well as a number of other factors known to be important to the success of prostate surgery such as the volume of Gleason grade 4 cancer, a potentially aggressive form of the disease. They then determined whether these cancer-related factors were associated with PSA levels measured in the patients prior to surgery. The research team found that pre-surgery PSA was not a useful predictor of any of the measured characteristics of the cancer. They also showed that surgical cure rates in men with PSA less than 4 ng/ml and men with levels as high as 10 ng/ml were no different. The bottom line is that prostate cancer, like all other cancers, cannot be detected at an early stage by a blood test, Stamey said. "What we need is a new marker, especially one that might reflect the high-grade cancers," he said. For every 10 percent increase in these high-grade tumors, the success rate of prostate surgery declines by 10 percent. Stamey's research lab is searching for better markers based on the genes expressed in high-grade prostate cancers. The work was funded in part by the Lucas Foundation in Menlo Park, Calif. |
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