Prostate Cancer Over-Diagnosed: Study
MONDAY, Aug. 31 -- Mass screening for prostate cancer with a test for prostate-specific antigen (PSA) has led to mass over-diagnosis and over-treatment, a new study contends.
Since the PSA screening test came into use in 1986, federal government data show that the number of prostate cancer cases in the United States has risen substantially, said the report in the Aug. 31 online issue of the Journal of the National Cancer Institute.
Treatments for prostate cancer include surgery and radiation therapy, and possible side effects are incontinence and impotency.
"The ideal screening test would have no effect on the number of cases," said study co-author Dr. H. Gilbert Welch, a professor of medicine at the Dartmouth Medical School's Institute for Health Policy and Clinical Practice. "It would change the time in life that the cancers were diagnosed, but not the number. Instead, there has been a sustained change in the number of cases -- 1.3 million more that would not have been diagnosed previously."
The death rate from prostate cancer has fallen in the United States, but not necessarily because of mass screening, Welch contended. "There are a number of reasons why mortality might fall, but the most obvious is that we have better treatment," he said. "Even without early detection, I expect mortality would fall."
Results of a European study reported earlier this year indicated that "to save the life of one man, 50 must be over-diagnosed," he said.
Guidelines for screening for blood levels of PSA -- a protein produced by the prostate gland -- differ widely. The American Cancer Society says that a PSA test should be offered at age 50, accompanied by an explanation of the potential benefits and hazards. The American Urological Association recommends a first PSA test at age 40, with follow-ups depending not only on the test score but also on factors such as ethnicity.
"The recommendations on this are all over the map, and that's because it's a close call," Welch said. "Different people look at the numbers and come to different conclusions. There is the potential to help some people and hurt some people."
In his own medical practice, Welch said, "I try to stay away from this one. If someone asks me, I explain the risks and the benefits."
Given the unknowns, it's entirely appropriate for a man to decide on having a PSA test without advice from a physician, Welch said.
But Dr. Judd Moul, director of the Duke University Prostate Center, after reading the new study, said, "This is not going to change my mind on the issue of screening." Moul recommends an initial PSA test at age 40, with follow-up if necessary.
"We now do have the potential for over-detection, but we still have 30,000 men a year dying from prostate cancer, and the best way to prevent deaths from prostate cancer is still screening," Moul said.
Both Moul and Welch agree that the PSA test is decidedly imperfect because it can't distinguish between the majority of prostate cancers that grow so slowly that they are no danger to a man's life and the fast-growing minority that are potentially fatal and require decisive treatment.
"Right now we don't have that magic biomarker," Moul said. "So I think it is more important to try to reduce the number of deaths than to worry about over-detection."
"I wouldn't expect one to come soon," Welch said, referring to a specific test for virulent prostate cancer. "So we will continue to find a lot of it, and a lot of it that doesn't matter."
Posted: August 2009
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