Interval cancers in the Antwerp European randomised study of screening for prostate cancer study, using a 6 year screening interval

Background: The European randomised study of screening for prostate cancer (ERSPC) was initiated to evaluate the effect of Prostate Specific Antigen (PSA) screening on prostate cancer mortality. Variations in screening modalities between participating centres, such as the interval between screening rounds are likely to affect the outcome of screening. Methods: The study describes the number and characteristics of interval cancers in men in the screening arm of the Antwerp ERSPC aged 55-65 years at the time of randomisation and participating in the screening rounds they were invited for. The interval between the first screening rounds was 6 years on average. Interval cancers were defined as cancers diagnosed during the screening interval but not detected by screening. Cases with a positive screening test were considered as interval cancers if diagnosis through biopsy occurred more than 1 year after screening. Interval cancer cases were identified through linkage with cancer registries. Aggressive interval cancer was defined as cancer with at least one of the following characteristics: stage M1 or N1, Gleason score higher than 7 or World Health Organisation (WHO) score of 3. Results: The 10 year cumulative incidence of interval cancers was 3.0% (n = 50) and the cumulative incidence of aggressive interval cancers was 0.5% (n = 8). During the first screening interval 36 interval cancers were detected. Of these 20 (55.6%) were detected more than 4 years after the initial screening and 5 (13.9%) were considered aggressive. All aggressive interval cancers emerged more than 4 years after initial screening. Conclusion: The occurrence of interval cancers in this study was higher than in the ERSPC centres that used a shorter screening interval. Aggressive interval cancers only started to emerge 4 years after initial screening.

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