Mammographic breast density over time among women who have participated in BreastScreen Norway

Abstract

Background: We analyzed the consistency in absolute and percent density using an automated method for estimating volumetric breast density among women who attended BreastScreen Norway 2007-2015. Material and Methods: We used information from 33,711 women aged 50-69 who underwent two to five full field digital screening examinations biennially, 2007-2015. BMI and HT-use was obtained from a self-administered questionnaire, sent together with the invitation to screening. BMI was categorized into <21.0; 21.0-24.9; ≥25.0 kg/m2, while use of HT was defined as ever versus never used. An automated method estimated fibroglandular volume (cm3), breast volume (cm3) and volumetric breast density (%) for each screening examination. We applied mixed-effects linear models to estimate associations between age, fibroglandular volume, breast volume and volumetric breast density over time including data on BMI and HT. Results: The results models indicated age to be associated with decreased fibroglandular volume and volumetric breast density, and increased breast volume. BMI <21 kg/m2 was associated with higher volumetric breast density, but lower fibroglandular and breast volume. Contrary, BMI ≥25 kg/m2 was associated with lower volumetric breast density and higher fibroglandular and breast volumes. Variation in volumetric breast density and fibroglandular volume within women was rather subtle: this variance did not exceed 10% for either volumetric breast density, fibroglandular volume or breast volume. Conclusion: Automated measures of volumetric breast density and fibroglandular volume software decreased with age among women screened in BreastScreen Norway. Absolute and percent density varied with a maximum of 10% over time, from first to last screening examination.