A team of researchers led by Johns Hopkins finds most men between 50 and 70 don't need an annual prostate specific antigen (PSA) test for prostate cancer because their risk of having a noncurable cancer that can be detected is so small.
"Many men need to be tested only once every two years, a change that could dramatically reduce the costs of prostate cancer screening in the United States," says H. Ballentine Carter, M.D., associate professor of urology at the Johns Hopkins Brady Urological Institute.
The study, published in the May 14 issue of the Journal of the American Medical Association, showed PSA testing every two years is sufficient to identify most men with curable prostate cancer even when a digital rectal examination (DRE) does not. During DRE, a physician feels the prostate and notes any abnormal swelling, which may represent cancer. PSA is a protein made by the prostate gland. Elevated levels of PSA in the blood indicate that prostate disease is present, but PSA levels alone do not prove whether the gland is cancerous.
"Our results suggest that annual testing for PSA in all men is not a cost-effective way to catch prostate cancer at an early, treatable stage," says Carter. The study was co-authored by researchers from the National Institutes of Health's National Institute on Aging (NIA) in Baltimore and Merck Research Laboratories (Blue Bell, Pa.)
Yearly PSA testing of men increases the number of results that falsely identify men with high levels of the protein, and may lead to further unnecessary tests, according to Carter. But reducing the frequency of testing also may leave some men with unidentified prostate cancer that would be caught by PSA testing.
The study concluded, however, that if a man's PSA level is less than 2 nanograms per milliliter at the first test, he isn't likely to develop incurable prostate cancer before being tested again in two years. A nanogram is a billionth of a gram (2 nanograms = 0.07 ounces). "Annual retesting in these men is not likely to save lives," says Carter. "So for these men, it's safe to wait an extra year. And because 70 percent of men age 50 to 70 have PSA levels less than 2, we can eliminate a lot of unnecessary testing."
"It was important to differentiate between important and unimportant cancers," says Carter. "Most men who die in their 90s have unimportant cancers in their prostate. These are cancers that have been growing extremely slowly, were never a threat to life and didn't require treatment."
"This study allows physicians to reduce the number of PSA tests that are being done unnecessarily," says Jay D. Pearson, Ph.D., senior epidemiologist at Merck Research Laboratories in Blue Bell, Penn. "PSA can be tested less frequently in men with PSA lower than 2 because there is little benefit to the patient and little chance of missing a curable cancer," says Pearson, a guest researcher at NIA.
The researchers also found that 89 percent of men with PSA levels between 4.0 and 5 micrograms per milliliter (1 microgram = 1 millionth of a gram) had curable cancers that required treatment, even though digital exams did not find the cancer. In addition, small, unimportant cancers not needing treatment were detected only 33 percent of the time.
"This means that a physician can feel confident that a man with a PSA between 4 and 5 who has prostate cancer, most likely has curable disease." says Carter. "But at the same time, the probability is small that the cancer is unimportant."
In the first part of the study, researchers measured PSA levels in blood samples of 40 men with prostate cancer from the Baltimore Longitudinal Study of Aging (BLSA), an ongoing, long-term study of aging conducted by the National Institute on Aging. These results were compared with blood samples from 272 men with no evidence of prostate cancer. The findings were used to determine how likely it was that men with a particular PSA level would have an increase in their PSA level. In a second part of the study, researchers determined the actual severity of prostate cancer at particular PSA levels in 389 men by analyzing information collected during and after surgery to treat the cancer at The Johns Hopkins Hospital.
Other authors of the study include Jonathan I. Epstein, Daniel W. Chan (Johns Hopkins); and James L. Fozard (Gerontology Research Center, National Institute on Aging, Baltimore).
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