The study suggests that doctors need better tests before they can recommend large-scale screening, study co-author Dr. Mattias Johansson told Reuters Health. "In particular, tools that help distinguish rapidly growing and potentially lethal tumors from slow growing tumors are warranted in order to minimize overdiagnosis and overtreatment."

Johansson, from the International Agency for Research on Cancer in Lyon, France, and his colleagues looked at more than 500 men with prostate cancer and more than 1000 case without it with similar characteristics.

They found that prostate-specific antigen (PSA) - a common blood test used to detect the disease - could not reliably distinguish between slow-growing prostate cancers that were not likely to cause any harm, and those that were likely to become aggressive and deadly.

The authors did, however, find that a very low PSA level -- below 1.0 nanograms per milliliter of blood -- virtually rules out prostate cancer. Given that many men would have higher values, however, it would be unclear what to do with many results.

In an analysis accompanying the study in the BMJ, Dr. Jennifer Stark, from Harvard School of Public Health, Boston, and colleagues examined the benefits and harms of PSA screening and concluded that at present there is simply not enough data to support population-based screening.

Moreover, they note, further studies with more precise measures are needed to gauge the financial and psychological toll of false positive PSA results, overdiagnosis, and overtreatment of prostate cancer.

Before men undergo PSA screening, they should be fully informed of the benefits, harms, and uncertainty associated with the test, Dr. Stark and colleagues emphasize.

SOURCE: BMJ, Online First September 25, 2009.