MONDAY, Sept. 8 (HealthDay News) -- Taking aspirin or other commonly used painkillers can lower blood levels of prostate-specific antigen (PSA) and possibly confuse the results of a common screening test for prostate cancer, a study finds.

Data on 1,319 men in a national health study showed that men who took non-steroidal anti-inflammatory drugs (NSAIDs) had PSA levels about 10 percent lower than men who didn't take the drugs.

A similar lowering effect was seen for regular use of acetaminophen (Tylenol), although it did not reach statistical significance.

It's also possible that the lowered PSA levels indicate that regular NSAID use reduces the risk of prostate cancer, the report said, citing studies showing a relationship between NSAID use and lower incidence of the cancer. The new study results "are consistent with previous reports that NSAID use is a protective factor for the development of prostate cancer," the researchers wrote.

"This raises questions that will have to be answered in a larger clinical trial," said Dr. Eric A. Singer, chief resident in urology at the University of Rochester, New York, and lead author of the report, which is in the Sept. 8 issue of Cancer.

Until now, the only drugs known to affect PSA levels were those used to treat an enlarged prostate, Singer said. "Other than that, PSA levels are not usually interpreted with medications in mind, so that raises that question," he said.

PSA screening tests commonly are done in the offices of primary care physicians, Singer said, and those doctors usually have information on which medications a man is taking. Whether men should be asked about NSAID use isn't clear now, he said.

"In terms of changing medical practice, I don't think so right now, not on the basis of this study," Singer said.

He and his colleagues are exploring the possibility of a trial that might clarify the issue, he said. Such a trial would follow men who regularly take NSAIDs and see how they affect the risk of prostate cancer.

"It is a trial that would go on for many years involving many men," Singer said.

NSAIDs reduce inflammation, and chronic inflammation has been linked to many malignancies, including prostate cancer. The cyclooxygenase enzymes, which are inhibited by NSAIDs, play an important role in inflammation.

"I would be very cautious about drawing any conclusion about what message men should take away from this study," said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society. "We should not take aspirin or NSAIDs as protection against prostate cancer."

The cause of the lower PSA levels is not clear, Lichtenfeld said. "Whether it is because the medicines have a positive effect in reducing the risk of prostate cancer or mask a possible sign of prostate cancer is unknown," he said.

Doctors should ask men about aspirin and NSAID use before PSA screening, Lichtenfeld said. "Doctors should ask patients about all their medications, prescription and over-the-counter," he said. "That conversation should always occur between health-care providers and their patients."

More information

Learn all about prostate cancer from the National Cancer Institute.