FRIDAY, Aug. 6, 2010 (HealthDay News) -- Some of the most widely prescribed drugs in the United States may skew results of prostate cancer screening tests, possibly causing errors in diagnoses, a new study finds.
A prostate cancer diagnosis is typically based on an elevated PSA (prostate-specific antigen)level, but new research shows that common drugs, including cholesterol-lowering statins and certain painkillers, may lower PSA levels.
"Our study reveals that men regularly consuming NSAIDs [non-steroidal anti-inflammatory drugs], statins, and thiazide diuretics may have lower serum PSA levels compared to men who are not taking these medications," said Dr. Steven L. Chang, lead author of a paper published online Aug. 2 in the Journal of Clinical Oncology.
"This could be a confounder when you're trying to screen for prostate cancer," added Dr. Lionel L. Bañez, assistant professor of urologic surgery at Duke University Medical Center in Durham, N.C. "We should exercise caution in interpreting PSA results from patients who are taking any of these medications, especially those who are taking these medications for a long time."
But for now, men shouldn't worry unduly that their health is being compromised, said another expert.
"One PSA reading does not give accurate information," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "You want to follow the trend over a number of years. It's time that makes a difference."
Other studies have suggested that these drugs as well as others used to treat enlarged prostate can lower PSA levels, but those studies suffered from various limitations, the authors reported.
Chang and his colleagues studied the effect of 10 common medications on PSA test readings in 1,864 men age 40 and older with no history of prostate cancer.
One year of using NSAIDs, statins or thiazide diuretics gave PSA readings 1 percent, 3 percent and 6 percent lower, respectively, than those for men not on one of these drugs.
The numbers were significantly higher after five years: 6 percent, 13 percent and 26 percent lower PSA levels, respectively.
When statins were combined with the diuretics over five years, PSA levels were lowered 36 percent, the researchers found. (But taking calcium channel blockers -- often prescribed for high blood pressure -- neutralized that effect.)
It's not known why these three classes of medications have this effect, but the finding merits further study, the researchers said.
"The reason why these medications are associated with a lower PSA are unclear, and therefore it is impossible at this time to determine the true implications of our findings," said Chang, who conducted the study while at the Stanford University School of Medicine but is now affiliated with Brigham and Women's Hospital and Harvard Medical School in Boston.
Given how many older men take one or more medications, and often take NSAIDs, statins, or thiazide diuretics, the findings could affect a vast number of people, the authors stated. (The American Urological Association recommends offering prostate cancer screening to men starting at age 40.)
"If future studies show that the difference in PSA has no bearing on the development of prostate cancer, then it may be necessary to lower the PSA threshold for recommending prostate needle biopsies in men who are taking NSAIDs, statins and thiazide diuretics," Chang said.
Another possibility is that these drugs may actually have a protective effect against cancer, researchers speculated.
"Should studies demonstrate that these medications reduce the risk of developing prostate cancer, then there may be some role for NSAIDs, statins and thiazide diuretics in prostate cancer prevention," said Chang.
NSAIDs and statins are already being studied as a means of preventing prostate cancer or its progression, Bañez said.
"There may be another story here," he said.
The National Cancer Institute has more on PSA testing.