To the Editor: Dr Buys and colleagues assessed the effect of ovarian cancer screening on mortality.1 The study had adequate power, defined end points, extensive follow-up, comprehensive outcome review, and minimal contamination in the control group. However, there are important limitations to the study design.
First, there was significant dilution of the screening effect. Women were screened for 4 to 6 years with a median follow-up of 12.4 years. This resulted in 86 of 212 cancers (40.6%) in the study group being diagnosed after screening ended, with those diagnosed more than 2 years after screening unlikely to have been affected by screening. The lower-than-expected adherence added to this dilution effect. Despite lack of power, a useful analysis would be to limit follow-up to 2 years after screening and compare deaths 8 years after randomization.