Getting screened for prostate cancer won't save men 75 and older from dying of the disease, according to doctors reporting today on a massive federal study of the usefulness of a popular blood test to measure prostate-specific antigen (PSA).

"If the man sitting in front of me was an elderly man with medical conditions and seemed to have a limited life expectancy — a seven-to-10-year  time frame — in good conscience I could tell that man I don't think a PSA test is absolutely necessary for him," study co-author Gerald Andriole, chief urological surgeon at Washington University School of Medicine in St. Louis, said during a press telebriefing yesterday.

"Men with longer life expectancy, I'm not confident we can say at this point what to do with them," Andriole said. "For younger men, it's still going to be worthwhile to get information from a PSA test" — but, he added, not necessarily the "knee-jerk," aggressive treatments common in the U.S. such as prostate removal, radiation and hormone therapy that can cause impotence and incontinence.

The findings, published online today in the New England Journal of Medicine, are based on up to 10 years of follow-up of nearly 77,000 men ages 55 to 74, half of whom received annual PSA tests for six years and four annual digital rectal exams, and half of whom received what was dubbed "usual care" from their own doctors (physicals that in some cases included PSA tests). Seven years out, those who got the annual screens had 22 percent more tumor diagnoses than those in the usual-care group, and 17 percent more after a decade.

But screening didn’t reduce the rate of death from the disease; in fact, among those who had prostate cancer a decade into the trial, more from the screening group had died of non-prostate-cancer causes than those in the control group. "The excess in the screening group was possibly associated with overdiagnosis of prostate cancer," according to the study.

That's sobering news after two decades of widespread PSA screening campaigns, when mortality from prostate cancer fell by 4 percent annually but diagnoses surged. While the doctors didn’t directly answer a question yesterday about whether the tests had harmed men, there is "no question there are men getting the side effects [of treatment] without getting any benefit," said study co-author Edward Gelmann, a professor of medicine at Lombardi Cancer Center at Georgetown University in Washington, D.C.

Though the scientists said that their results were "definitive," another large study conducted in Europe, also published in the NEJM today, found that PSA testing cut the risk of prostate cancer death by 20 percent. That research, the European Randomized Study of Screening for Prostate Cancer, also found that screening led to the diagnosis of 40 percent more cancers in men 50 to 74.

Gelmann insisted that the differing results shouldn’t be interpreted as conflicting. The Europeans were screened every other year for four years, the cutoff for what was deemed elevated PSA levels was lower (three there vs. four in the U.S.), the population was different (white vs. 15 percent minority in the U.S.) and men there may not have been treated as aggressively.

"The jury is definitely out about differences between the two trials," Gelmann said.

Image of prostate cancer awareness ribbon by iStockphoto/Joe Belanger