Currently, prostate cancer risk in middle-aged and older men is partly determined by a blood test for total prostate-specific antigen (PSA). A new test also measures blood PSA, but only the percentage of PSA that is "free" or not bound to other proteins. Using the two tests together, physicians may be able to further refine their estimations of an individual patient's risk of prostate cancer, and reduce the number of prostate biopsies performed by as much as 20%, or about 120,000 biopsies per year in the US alone.
The researchers found that by using an upper cutoff of 25% free PSA, they could correctly identify 95% of the men in this group who had prostate cancer while reducing the number of unnecessary biopsies performed by approximately 20%. Moreover, the percentage of free PSA was a stronger predictor of the presence of prostate cancer than were two traditional risk factors, total PSA and age, in this group of patients.
However, by definition, its 95% sensitivity implies that 5% of patients with prostate cancer would be missed using such a test. The cancers missed were most often in older men with larger glands, who tended to have less aggressive disease. The investigators note that these patients are often not affected by or treated for prostate cancer.
If the free PSA measurement is outside the 25% cut-off, urologists can have a fair amount of confidence that they're not missing an underlying cancer. A prostate biopsy costs about $1,200. The anticipated cost of both total and free PSA tests is $130, a considerable financial saving where applicable.
The Journal of the American Medical Association May 20,1998;279:1542-1547
COMMENT: As mentioned in newsletter #40, the FDA approved this test. The test has been available for a few years but the FDA approval now means that insurance companies will likely pay for it. It is a great test for diagnosing prostate cancer. I would also review issue #34 and #41 for more information on treatment of prostate cancer.