Prostate Cancer Biomarker
Measuring prostate specific antigen levels as a method of screening for prostate cancer is now “all but useless,” according to researchers from Stanford University, and many men with prostate cancer should not undergo radiation therapy or surgical removal of the prostate.
The investigators gathered preoperative PSA testing for prostate cancer measurements from 1,317 patients who underwent radical prostatectomies since August 1983 and compared those results with postoperative measures of disease severity, including the volume of the largest cancer removed and the percent of that cancer that was classified as Gleason grade 4/5.
Results showed that during the five-year period from Aug. 24, 1983, to Dec. 31, 1988, approximately 44 percent of the cases showed a relationship between PSA level and the size of the largest cancer removed from the patient. In comparison, only 2 percent of cases showed such an association during the five-year period from Jan. 1, 1999, to July 1, 2003.
Prostate Size and PSA Linked
Furthermore, during the earliest period, six histological cancer parameters were significantly associated with serum PSA, but during the most recent period, only prostate size was associated with PSA level. An increase in prostate size (known as benign prostate hypertrophy, or BPH) is not indicative of prostate cancer, the study authors noted.
The investigators postulated that the decline in usefulness of PSA screening is due to the widespread use of the test. Because of the frequency of such testing, tumors are typically detected at much earlier stages and are much smaller than they were 20 years ago. As a consequence, the tumors do not generate enough PSA for the test to be a good measure of severity.
The authors noted that prostate cancer can now be detected in virtually all men.
“On the surface, this would appear to be a great epidemiological accomplishment, except for the disturbing fact that while prostate cancer is a ubiquitous tumor, it has an extraordinarily small death rate of 226 per 100,000 men older than 65 years,” they said in the October issue of The Journal of Urology.
According to lead investigator Dr. Thomas Stamey, all men will develop prostate cancer if they live long enough, but the low mortality rate means that only aggressive cancers need to be treated.
“Our job now is to stop removing every man’s prostate who has prostate cancer,” Stamey said in a Stanford press release. “We originally thought we were doing the right thing, but we are now figuring out how we went wrong. Some men need prostate treatment, but certainly not all of them.”
Stamey added that cancers detected through digital rectal examination are always significant tumors that require treatment, but a serum marker for prostate cancer that is proportional to the volume and grade of the cancer is urgently needed.
According to the investigators, PSA tests are now only useful as a marker of BPH and of failure to cure a patient of prostate cancer.