WEDNESDAY, May 26, 2004 (HealthDayNews) -- In a study that further questions the validity of the current PSA test, researchers found that up to 15 percent of men with what were considered "normal" PSA levels actually had prostate cancer.
PSA (prostate-specific antigen) levels are routinely used to screen men for the presence of prostate cancer. Typically, levels above 4 ng per milliliter indicate the need for a biopsy to check for any malignancies.
A debate has been circulating as to whether the current threshold is inadequate. For some, the latest findings, appearing in the May 27 issue of the New England Journal of Medicine, may emphasize the need to lower the upper limit for normal.
Others feel differently. "I don't think there's enough evidence that I would be comfortable with signing in on and agreeing that we should lower the PSA to 2.5 as a new upper limit of normal," said Dr. Simon Hall, director of the Deane Prostate Health and Research Center at Mount Sinai Medical Center in New York City.
The advent of PSA screening increased the detection of prostate cancer, according to the study authors. But even from the early days, experts have been divided over how useful the test is in detecting significant cancers.
Even with the current threshold, Simon pointed out, there is an overdiagnosis rate of about 20 percent.
"We're starting to diagnose more cancer, but the issue is whether these are clinically significant cancers," he said.
The authors of this study looked at 2,950 men who had been in the placebo arm of the recent Prostate Cancer Prevention Trial. That study looked at whether the baldness drug finasteride could prevent prostate cancer.
None of the men in this group had a PSA level above 4 or an abnormal digital rectal examination, but all had a biopsy at the end of the seven-year study. The PSA test had to have been performed within 90 days before the biopsy.
Among these men, 15.2 percent were diagnosed with prostate cancer and 14.9 percent had a Gleason score of seven or higher; the higher the score, the more difficult the cancer is to treat.
The prevalence of cancer increased as the PSA scores went up. Some 6.6 percent of men who had a PSA level of 0.5 ng per milliliter or lower had cancer; 10.1 percent of men who had PSA levels of 0.6 to 1.0 had cancer; 17 percent of those with PSA levels of 1.1 to 2 had cancer; 23.9 percent of those with PSA values of 2.1 to 3 had cancer; and 26.9 percent of those with values of 3.1 to 4 had cancer.
The prevalence of more serious cancers increased from 12.5 percent of cancers associated with a PSA level of 0.5 ng per milliliter or less to 25 percent of cancers associated with a PSA level of 3.1 to 4.0 ng per milliliter.
Men who have scores lower than 4 who also have strong family histories of prostate cancer may want to consider a biopsy, said study author Dr. Ian Thompson, chief of urology at University of Texas Health Science Center at San Antonio. The rate of increase of PSA levels also bears watching, he added.
As for a universal lowering of the threshold for normal, the author of an accompanying editorial says no, for several reasons. One is that the prostate cancers detected at lower PSA levels are likely to be "clinically insignificant." Another is that even treating these cancers at these early levels does not necessarily guarantee a better outcome.
What the field really needs are new biomarkers to both predict and assess prostate cancer, Thompson said.
"The ideal biomarker for me is a test that in a man who has no cancer it's negative, and in the man who has cancer that will never cause him problems, it's also negative, but is positive in a man with cancer that poses him a risk," Thompson said. "That test is positive while the cancer still can be cured."
For more on prostate cancer, visit the Prostate Cancer Research Institute.