PLCO update suggests positive predictive value of prostate screening drops over time
(18 January 2009: VIDYYA MEDICAL NEWS SERVICE) -- In the most recent update of prostate cancer screening data from NCI’s PLCO trial, the number of positive screening tests among the more than 38,000 men enrolled in the intervention arm has remained consistent during the 4 years of study. However, the positive predictive value of these tests—that is, the ratio of true positives to the total number of true and false positives—decreased over time. The full report appeared in the December issue of the British Journal of Urology International.
Researchers attributed this decrease in the positive predictive value from baseline screening, which was 17.9 percent, to the subsequent annual screens, which ranged from 10.4 percent to 12.3 percent, to the fact that initial screening identified many of the cancers and left men with elevated prostate-specific antigen (PSA) levels but negative biopsies to be identified in subsequent screening rounds. The cancers found at baseline were more likely than those found in subsequent screenings to be advanced stage (5.8 versus 2.9 percent) and to have a Gleason score of 7 to 10 (34 versus 25.5 percent).
PLCO is one of two major ongoing trials expected to show whether screening for prostate cancer saves lives. The other is the European Randomized Study of Screening for Prostate Cancer (ERSPC), which screens participants less frequently, at 2- and 4-year intervals. In a related commentary, ERSPC director Dr. Fritz H. Schröder addressed the issue of more aggressive prostate cancer, noting that the data in both trials “suggest that certain cancers escape screening irrespective of the screening interval used.”
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