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Two large-scale randomized screening trials, the Prostate, Lung, Colorectal and Ovary (PLCO) cancer trial in the USA and the European Randomized Screening for Prostate Cancer (ERSPC) trial in Europe are currently under way, aimed at assessing whether screening reduces prostate cancer mortality. Up to the end of 1998, 102,691 men have been randomized to the intervention arm and 115,322 to the control arm (which represents 83% of the target sample size) from 7 European countries and 10 screening centers in the USA. The principal screening method at all centers is determination of serum prostate-specific antigen (PSA). The PLCO trial and some European centers use also digital rectal examination (DRE) as an ancillary screening test. In the core age group (55-69 years), 3,362 of 32,486 men screened (10%) had a serum PSA concentration of 4 ng/ml or greater, which is 1 cut-off for biopsy (performed in 84%). An additional 6% was referred for further assessment based on other criteria, with much less efficiency. Differences in PSA by country are largely attributable to the age structure of the study population. The mean age-specific PSA levels are lower in the PLCO trial (1.64 ng/ml [in the age group 55-59 years], 1.80 [60-64 years] and 2.18 [65-69 years) than in the ERSPC trial (1.28-1.71 [55-59], 1.75-2.87 [60-64] and 2.48-3.06 [65-69 years]). Detection rates at the first screen in the ERSPC trial range from 11 to 42/1,000 men screened and reflect underlying differences in incidence rates and screening procedures. In centers with consent to randomization design, adherence in the screening arm is 91%, but less than half of the men in the target population are enrolled in the trial. In population-based centers in which men were randomized prior to consent, all eligible subjects are enrolled, but only about two-thirds of the men in the intervention arm undergo screening. Considerable progress has been made in both trials. Enrollment will be completed in 2001. A substantial number of early prostate cancers have been detected. The differences between countries seem to reflect both underlying prostate cancer incidence and screening policy. The trials have the power to show definitive results in 2005-2008., (Copyright 2002 Wiley-Liss, Inc.)