Long-term changes in breast density reporting after implementation of BI-RADS 5 ^th edition guidelines

Objectives: The objectives of the study are to investigate if there is a long-term change in density assessment between the 4 th and 5 th Editions of Breast Imaging Reporting and Data System (BI-RADS). Specifically, to assess the density reporting patterns of radiologists at a single institution several years after changes were made in density assessment criteria in BI-RADS 5 th Edition, which focused on masking effect of tissue and removed the percent-density value system as a criterion for density assessment. Material and Methods: Health Insurance Portability and Accountability Act (HIPAA) compliant, single institution study where mammographic density data were obtained for 4 years before the BI-RADS 5 th Edition change and 4 years after it. The total sample size was 132,326 mammograms. Comparison of non-dense versus dense breast categories was specifically made to evaluate any changes that could have led to a change in the needs for supplemental screening after the new guidelines. Chi-square tests were used to evaluate the distribution of density type among mammograms evaluated before and after the new guidelines were implemented. Statistical significance was considered at the α = 0.05 threshold, and two-sided p -values are reported. Results: After implementation of the 5 th Edition, there was an overall increase in mammograms described as dense (39.1%) compared to the old guidelines (38.4%, p = 0.01); however, the effect size of this difference was statistically significant but of negligible practical magnitude (Phi = 0.01). Conclusion: This large single-institution analysis demonstrates that the adoption of the BI-RADS 5 th Edition Density Assessment Guidelines has led to a modest but sustained increase in the proportion of mammograms categorized as dense. While the effect size is small, even slight shifts in density classification may influence patient management and supplemental screening utilization in the new era of mandatory breast density notification.