In this excerpt from a recent issue of Health After 50, H. Ballentine Carter, M.D., Professor of Medicine at the Johns Hopkins Hospital, discusses current trends in PSA testing.
Since the prostate specific antigen (PSA) test became widely used in the 1990s, prostate cancer deaths have dropped dramatically. Today one of the biggest problems with PSA testing is that it detects many cancers that are not life threatening and would never have been diagnosed or treated otherwise, especially among older men.
Q. How does PSA testing result in overdiagnosis?
Dr. Carter: PSA levels are most often elevated for reasons other than cancer, such as prostatic enlargement (benign prostatic hyperplasia -- BPH) or prostatic inflammation, which are common among aging men. In addition, many men with these conditions also have small prostate cancers that are also common with age but usually do not progress.
The PSA test cannot differentiate between dangerous cancer and benign conditions, so when biopsies are based on elevated PSA test results, prostate cancers are often found serendipitously; many of these would not have been found otherwise. This over diagnosis of prostate cancer has been estimated to occur in 30–50% of men between ages 55 and 80 years. Over 85% of prostate cancers detected are treated when diagnosed. Thus, over treatment of cancers that would not have caused harm is a byproduct of screening.
The extent to which PSA testing for the early diagnosis of prostate cancer results in more benefit (reduction of prostate cancer deaths) versus harm (detection and treatment of prostate cancers that would not have caused harm) is hotly debated. Nevertheless, physicians and patients prefer the risk of unnecessary treatment to missing a potentially lethal cancer. The solution to the dilemma is a test that can differentiate between life- threatening and indolent prostate cancer before a biopsy takes place.
Q. In the meantime, how are doctors trying to reduce the number of needle biopsies and over diagnosis?
Dr. Carter: Currently, annual PSA testing beginning at age 50 is recommended, but newer guidelines will stress the need for a baseline PSA test at age 40, another one at 45, and then an annual or biennial PSA test beginning at age 50 depending on the PSA level. By starting to accumulate a PSA history at age 40, a man will have measurements to compare with levels obtained in his 50s in order to determine the rate his PSA changed -- his PSA velocity—a useful measure of the presence of a life-threatening cancer.
PSA levels vary a lot over the short term (6 months). It is important to have a PSA history of more than two years to evaluate PSA velocity accurately. If PSA velocity is consistently above 0.4 ng/mL per year in a man with a PSA level below 4.0 ng/mL, prostate cancer should be suspected and a biopsy considered. In men with PSA levels between 4 and 10 ng/mL, a PSA velocity of 0.75 ng/mL per year suggests the presence of prostate cancer.
