But as per a study published in the Journal of the National Cancer Institute, frequent screening could of course help detect more tumors, but it failed to cut the number of aggressive tumors detected in between scheduled screenings.
Dutch and Swedish researchers tracked about 4,000 men Gothenburg, Sweden, and another 13,000 men in Rotterdam. They were 55 to 65 years old at the time of the first screening. While the first group was all administered prostate-specific antigen, or PSA, blood tests every two years the second every four years.
Over a 10-year period ending in December 2005, detection of any form of prostate cancer was higher among the Swedish men who were screened more frequently -- 13 percent -- compared to the Dutch men who were screened less often -- 8 percent.
But there was no statistically significant difference in the two groups in the number of aggressive tumors that appeared between the times when the tests were conducted. This showed that more frequent screening did not cut the number of these cancer cases as one might have expected, the researchers said.
Asked about the implications of the findings on how often men should be screened, study leader Monique Roobol of Erasmus Medical Centre in Rotterdam said, "That's a tricky question."
The researchers wrote that each PSA test may lead to prostate cancer diagnoses among some men who may have "clinically insignificant disease."
"We here in Europe feel that over-diagnosis and over-treatment is certainly something you should avoid," Roobol said in a telephone interview.
Diagnoses of prostate cancer have risen substantially since screening using PSA tests began in the late 1980s. While the death rate has dropped, it is unclear if this is a direct result of this screening, the American Cancer Society said.
The prostate is a walnut-sized gland that makes fluid for semen. PSA is a substance produced by the prostate.
The American Cancer Society recommends doctors offer the PSA test or another screening method called DRE, or digital rectal exam, annually to men beginning at age 50.
The idea behind the screening is that the tests can detect tumors early on when they are easiest to treat. But, Roobol noted, screening also may detect minor tumors that may pose no threat but end up getting unnecessarily aggressive treatment.
Screening generally is less frequent in Europe. Most institutions taking part in a large European study assessing prostate cancer gave the tests to men every four years.
"Although many of us believe that early detection is saving lives, definitive evidence is lacking," Dr. David Crawford of the University of Colorado Health Sciences Center wrote in an editorial accompanying the study.
"Critics of the four-year screening interval have voiced concerns that clinically significant cancers could be missed by such an extended interval," Crawford added, saying he was not convinced that the new study has allayed these fears.
The World Health Organization said the results of studies already underway into the effectiveness of prostate cancer screening are needed before making any recommendation.