Should We Adjust Visually Assessed Mammographic Density for Observer Variability?

This study aimed to determine whether correcting for observer variability alters estimations of breast cancer risk associated with mammographic density. A case control design examined the relationship between mammographic density, measured by visual analogue scales (VAS), and the risk of breast cancer after correcting for observer variability. Mammographic density was assessed by two observers and average scores (V2) were adjusted to correct for observer variability (V2(ad)). Two case-control sets were identified: (i) breast cancer detected during screening at entry and (ii) breast cancer detected subsequently. Cases were matched to three controls. In the first case-control set the odds ratio for breast cancer was 4.6 (95 %CI 2.8-7.5) for the highest compared to the lowest quintile of V2, and was attenuated for V2(ad) (OR 3.1, 95 %CI 1.9-4.8). Similar findings were observed for the second case-control set. Not adjusting for observer variability may lead to an overestimate of the risk of breast cancer.