TUESDAY, Oct. 31, 2006 (HealthDay News) -- Measuring changes in levels of prostate-specific antigen over time may be a more accurate way of identifying men at risk for aggressive prostate cancer, a new study suggests.
Prostate-specific antigen (PSA) is a protein produced by the prostate gland. The PSA test measures the level of PSA in the blood and is used to screen for prostate cancer. But test results can sometimes lead to treating cancers that would never become life-threatening. Studies have suggested that "PSA velocity" -- the rate that PSA levels increase -- is higher in men with life-threatening prostate cancer.
In their new study, Dr. H. Ballentine Carter of Johns Hopkins University School of Medicine and his colleagues contended that since PSA velocity is a good method for predicting prostate cancer, PSA screening should begin earlier to establish a baseline for evaluating changes over time.
The report is published in the Nov. 1 issue of the Journal of the National Cancer Institute.
"This is the first time that the rate of change in PSA has been shown to be a marker for identifying men who have a disease that is life-threatening at a time when the disease is still curable," Carter said.
In the study, Carter's team evaluated the PSA velocity of 104 men with prostate cancer who had not died from the disease, 20 men who had died of prostate cancer, and 856 men without prostate cancer.
The researchers found that PSA velocity 10 to 15 years before a cancer was diagnosed was linked to survival 25 years later. Specifically, patients with a lower PSA velocity had a 92 percent survival rate, but patients with a higher PSA velocity had a 54 percent survival rate.
In addition, men with a higher PSA velocity had a higher risk of dying from prostate cancer, compared with men with a low PSA velocity.
In the past, PSA levels have been used as a marker, or warning signal, for prostate cancer, and everyone has been treated exactly the same, Carter said. "Everyone who reaches a certain threshold value [typically 4.0 nanograms per milliliter of blood] has a biopsy. That results in over-diagnosis and over-treatment. This is a way out of that dilemma," he said.
Instead of performing a biopsy on every man who has a certain PSA level, PSA velocity can be looked at over time before deciding which men need a biopsy, Carter said. "This is the first time that we have strong evidence that we might be able to use PSA to identify men who really have life-threatening disease and treat them aggressively," he said.
Carter suggests that men have an initial PSA test at age 40 to establish a baseline. Then they can have another PSA tests every few years to see if the PSA level rises and at what rate. The more rapidly the PSA rises, the more likely it is that the cancer is life-threatening, he said.
"The history of PSA levels tells you more than any one level does," Carter said. "If it's low and remains low, testing could be done every other year after age 50. If it's rising, those people need a biopsy or need to be followed very carefully for changes in their PSA."
Timothy Church, a professor of medicine at the University of Minnesota School of Public Health and author of an accompanying editorial in the journal, thinks PSA velocity might be useful in evaluating prostate cancer risk. "PSA velocity may help doctors decide which prostate cancers do or do not need to be treated aggressively," he said.
However, Church cautioned that before PSA readings can be used in this way, the results of ongoing trials need to be known.
"There is promise that one day we will be able to use changing PSA values to help determine which cancers are aggressive and need to be treated aggressively and which cancers can be left alone for watchful waiting," he said.
Visit the U.S. National Cancer Institute for more on prostate cancer.