FRIDAY, Jan. 6 (HealthDay News) -- Annual screening for prostate cancer doesn't save lives, finds a new study that is unlikely to quell the controversy surrounding routine prostate specific antigen (PSA) screening.

"Organized prostate cancer screening when done in addition to whatever background testing exists in the population does not result in any apparent benefit, but does result in harm from false positives and over-diagnosis," said lead researcher Philip Prorok, from the Division of Cancer Prevention at the U.S. National Cancer Institute.

"Men considering prostate cancer screening should be fully informed of the implications of such testing before making a decision," he added.

Experts have disagreed for some time on whether the blood test saves lives or results in over-diagnosis and over-treatment. The new findings, which extend prior results out to 13 years of follow-up, are published in the Jan. 6 online edition of the Journal of the National Cancer Institute.

The study followed men enrolled in the Prostate, Lung, Colorectal and Ovarian Cancer Screening (PLCO) Trial from 1993 to 2009, comparing results for a group of men who had undergone screening with those for men who hadn't had testing. The men were 55 to 74 years old.

One group had PSA screening every year for six years and a digital rectal examination every year for four years. The other men had regular care, which in some cases included screening if requested by the patient or doctor.

Compared to men getting usual care, the screened men had a 12 percent relative increase in prostate cancer but a slightly lower rate of high-grade cancer.

However, no difference in deaths was seen between the two groups.

This finding held true even after age, screening before the trial and other medical conditions were taken into account, the researchers said.

Prorok said that better treatment for prostate cancer may explain the similar mortality results.

Among prostate cancer patients, death from other causes was somewhat higher in the screened group (10.7 percent of 4,250 men with prostate cancer) compared to the usual care group (9.9 percent of 3,815 men with prostate cancer).

This indicates men who underwent PSA screening were over-diagnosed, meaning the test picked up slow-growing tumors that probably weren't lethal, the researchers said.

"PSA testing and digital rectal examination screening as conducted in this trial did not reduce prostate cancer mortality, but there was a persistent excess of prostate cancer cases in the screened arm, suggesting over-diagnosis of prostate cancer," Prorok said.

Some prostate cancer experts disagree with the authors' conclusions.

Dr. Anthony D'Amico, chief of radiation oncology at Brigham and Women's Hospital in Boston, said the results are invalid because the trial was flawed.

According to D'Amico, 52 percent of those who received usual care had a PSA screening. "That's a serious issue which makes it very hard for the study to show if any benefit exists for PSA screening," he said.

Also, 15 percent of those who were supposed to get PSA screening never did, D'Amico said. "So what you've got is a screening study in which 85 percent of the people got PSA screened on the screening arm and 52 percent got screened on the control arm, which makes it impossible to ever measure a difference," he said.

Men should ignore this study, "because it has no relevance to PSA screening," D'Amico said.

D'Amico said he has more confidence in the results of a European study published in 2009 in the New England Journal of Medicine, which showed a 20 percent reduction in cancer mortality with PSA screening.

Men who can benefit most from screening are those at risk for prostate cancer, particularly men who have a family history of prostate cancer, African Americans and men over 60, D'Amico said.

Prorok acknowledged that the PLCO trial wasn't perfect. "Nonetheless, the contamination was not enough to eliminate the early diagnosis of prostate cancers nor the persistent excess of cancers," he said.

PLCO provides information about over-diagnosis, Prorok added. "Even if the contamination did dilute a benefit compared to no screening, the result of no mortality difference between the arms in PLCO could be interpreted to suggest that more intensive screening is not beneficial but does result in harm," he said.

More information

For more information on prostate cancer, visit the American Cancer Society.