A new study challenges the prevailing view of recent years that screening for prostate cancer does not reduce prostate cancer mortality. The researchers found significant benefit from screening versus no screening after reanalyzing data from two large studies that formed the basis of a 2012 recommendation by the U.S. Preventive Services Task Force (USPSTF) against routine screening using the prostate-specific antigen (PSA) blood test.

The USPSTF's recommendation, which was based on the two studies even though they had conflicting results, has led to a decreased use of the PSA test. The Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO), conducted in the United States, found no difference in prostate cancer mortality between 38,340 men who received PSA screening and 38,343 men in a control group. The European Randomized Study of Screening for Prostate Cancer (ERSPC), however, found a 21% reduction in prostate cancer deaths among 72,473 screened men, compared with the control group of 88,921.

The new study reanalyzed the PLCO and ERSPC data and found that in both trials, PSA screening was associated with reduced prostate cancer deaths but only after accounting for a significant problem within the PLCO study. The researchers found that 50% of the men assigned to the PLCO control group actually received at least one PSA screening during the study-in fact, many had more than one-through their routine medical care. This "contamination" minimized differences in prostate cancer mortality during follow-up between the screened and the control groups.

To correct for this flaw in the PLCO trial, the new study estimated the intensity of screening in each group relative to no screening and concluded that PSA screening reduced prostate cancer mortality by 25% to 31% in the ERSPC trial and by 27% to 32% in the PLCO trial.

A known drawback of PSA testing is the risk of false positives potentially leading to unnecessary diagnostic procedures and treatment. Some prostate cancers are "indolent," meaning they are slow growing and unlikely to lead to death or even to cause symptoms. How to use the PSA test to save lives while minimizing unnecessary treatment remains the challenge. The USPSTF is in the process of updating its recommendations on prostate cancer screening.-Joan Zolot, PA

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