11 months ago
(USA TODAY) -- Prostate cancer screenings given to millions of American men each year have little or no effect on whether patients will die from the disease, according to two large studies released Wednesday.
Although the new trials produced slightly different results, both raise the question of whether early detection of prostate cancer -- whose treatments can leave men impotent and incontinent -- does more harm than good.
Q&A: Should men still get PSA screenings or not?
After nearly a decade of follow-up, American scientists leading a trial of 77,000 men found there were slightly more deaths among men who were randomly assigned to undergo annual screening for PSA (prostate-specific antigen) as there were in the comparison group. Because prostate tumors usually grow so slowly, however, doctors say there haven't been enough deaths yet to know whether that small increase is a real problem or due to chance.
Europeans leading a trial of 182,000 men found modestly more positive results, with screening tests reducing the risk of death by 20%. Those findings just barely meet the standards for a real trend, however, and were statistically very close to being due to chance, says the American Cancer Society's Otis Brawley.
"If screening is beneficial, it is beneficial in a very small way," says Brawley, who wasn't involved in either study.
Others say the test, which has been widely used for 20 years, may have hurt many men.
"It's likely that thousands of men have been helped, but many more thousands of men have been harmed," says Ruth Etzioni, who studies prostate cancer risk at Seattle's Fred Hutchinson Cancer Research Center but wasn't involved in either trial.
Scientists at the National Cancer Institute, which funded the American study, say they will need to follow men for several more years before they will know with certainty whether PSA screening saves lives in the long run. That's because most prostate tumors grow very slowly, so that very few men die within 10 years of diagnosis.
Physicians around the world had hoped these two long-running trials would provide clear-cut advice to patients, Etzioni says.
For now, doctors can advise one group of men -- those with life expectancies under 10 years -- that it's probably safe to skip the PSA, since they are likely to die of something else before a tumor would cause them any harm, says Gerald Andriole of Washington University School of Medicine, lead author of the American paper. A government panel issued a recommendation last August that men age 75 and over shouldn't be screened.
Although more than half of American men have undergone a PSA and most view the test favorably, few are aware of the heated debate that has consumed doctors since the blood test was introduced two decades ago.
Proponents of screening say that the tests can find prostate cancers years before they would ever cause symptoms, when they're highly curable.
Critics, however, note that many prostate tumors don't need to be cured. That's because about half of prostate cancers grow so slowly that they never cause any harm, says Darmouth Medical School's H. Gilbert Welch, who worked on the American study.
Treating these harmless tumors doesn't help men -- since their lives were never at risk anyway -- but it can hurt them, he says. About 1 in 1,000 men who have prostate cancer surgery die while in the hospital, he says. And he cites research that shows half of those who have surgery are left with impaired sexual function and about a third suffer impaired urinary function. About a third who get radiation have rectal disfunction or chronic diarrhea.
Because doctors can't always tell which tumors are deadly, they tend to treat everyone aggressively, subjecting up to half of men to unnecessary surgery or radiation, Brawley says.
According to the European study, doctors would need to screen roughly 1,000 men for 10 years -- and treat about 50 of them unnecessarily -- to prevent one death from prostate cancer, Welch says. Men who opt for a PSA test should consider this risk, he says.
"The question for the patient is, 'Do you want to get into this gamble, when you are 50 times more likely to be overdiagnosed and treated needlessly than you are to have your life saved?' " Welch says.
Younger men should discuss the risks and benefits with their doctors, Andriole says. Brawley notes that screening remains important for men with strong family histories of prostate cancer or other medical conditions.
That advice puts too much of the burden on patients to sort through complex medical advice, Etzioni says. She says she's disappointed that men will have to wait several years for more definitive guidance.
Scientists already are looking for molecular markers of prostate cancer that would help doctors tell which cancers are aggressive and which can be ignored, says the NCI's Christine Berg, the American study's senior author.
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