Routine prostate cancer screening does not appear to help men live longer, according to a new study that pooled the best available data on the controversial topic.

U.S. federal experts and several medical associations discourage screening in men 75 years or older, but say the evidence is insufficient to make sweeping recommendations for younger people. Still, many U.S. doctors still test for the disease.

The new analysis, published in the journal BMJ, shows that testing will pick up the disease, detecting 20 cases for every 1,000 men screened. But it didn't alter overall death rates or the odds that men will die from prostate cancer.

Therefore, the 20 patients (in 1000) would be considered 'overdiagnosed,' said Dr. Philipp Dahm, of the University of Florida in Gainesville, who led the research.

He said screening was overused -- especially in older men and those with other diseases, who would be unlikely to be troubled by prostate cancer during their lifetime.

Prostate cancer guidelines across the globe and even within the US in fact vary considerably, he told Reuters in an e-mail. Ideally, evidence based individual decision-making and health policy decisions should be based on the current best evidence as provided by systematic review, which this study provides.

Dahm and colleagues analyzed data from six earlier studies, including more than 387,000 participants. Each had been randomly assigned to receive either no screening or a blood sample testing for prostate-specific antigen (PSA), which may hint the presence of a tumor. Some men in the screening group also had a rectal exam.

The researchers note that the quality of the evidence never went beyond moderate, and the studies varied in how long they followed the men, making them hard to compare.

While some of the data were conflicting, pooling them revealed no benefit at all from screening.

The reason that diagnosing prostate cancer doesn't affect life span may be that many tumors develop so slowly that they never cause any trouble.

On the other hand, prostate cancer treatments, including surgery or radiation, can lead to incontinence and erectile dysfunction in about a third of patients.

The current recommendation by the U.S. Preventive Services Task Force, a federally appointed expert panel, is for men to have a discussion of the pros and cons of screening with their doctors before deciding on what to do.

If screened, half of all 60-year-olds would have PSA levels so low that they wouldn't need additional testing, according to another study published in BMJ.

In that study, researchers followed more than 1,000 60-year-old Swedish men until they died or turned 85.

The PSA level at age 60 is highly informative about your risk of prostate cancer death and the risk that the cancer will spread, said Dr. Hans Lilja of Memorial Sloan Kettering Cancer Center in New York City, who led the study.

Lilja and colleagues found those with the highest PSA levels (the top quarter) accounted for nine in 10 prostate cancer deaths. Still, they noted, only one in six men in the top five percent of PSA had actually died from the disease by age 85.

That suggests that low PSA levels near the age of 60 might reassure patients that they don't need any further testing, said Lilja.

But that would still require at least one test, which may cost hundreds of dollars.

And as Dahm said, there is currently insufficient evidence to suggest that routine screening...reduces overall or prostate cancer-specific mortality.