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Breast density changes over time: Frequency, patterns, and practice implications.

e18772 Background: Dense breast tissue is known to obscure malignancy on mammography and is considered an independent risk factor for breast cancer. Because of its clinical significance, breast density has been incorporated into cancer risk assessment tools, supplemental screening recommendations, and patient notification laws. Changes in density—whether due to intrinsic changes in breast tissue over time or to inter-radiologist variability in interpreting mammographic results—can therefore have significant implications for patients. The purpose of this study was to quantify longitudinal patterns of breast density change. Methods: This retrospective cohort study tracked breast density changes among 37,156 patients who received multiple mammograms at a large academic medical center between October 1, 2015 and June 29, 2021. Breast Imaging-Reporting and Data System (BI-RADS) density categories A (least dense) through D (most dense), visually determined by radiologists at the time of screening, were abstracted from electronic medical records and dichotomized into one of two density statuses: non-dense (categories A and B) and dense (categories C and D). A sequence analysis of longitudinal changes between the two density statuses was performed using SQL. Results: The majority (91.3%, n = 33,920) of patients maintained the same density status (dense or non-dense) throughout the six-year study period, while 8.7% of participants (n = 3,236) experienced between one and six density status changes. Among patients who experienced any density status change, the vast majority (96.7%, n = 3,131) moved exclusively between BI-RADS categories B and C, the intermediate density categories (Table). Frequency of density status change was positively correlated with average number of mammograms performed per patient. Conclusions: Although most patients maintain a consistent breast density status, some will experience multiple status changes even over this relatively short timeframe (< 6 years), with more frequent changes being associated with more frequent mammograms. The overwhelming majority of patients whose density status changed moved exclusively between BI-RADS categories B and C, suggesting a role for inter-radiologist variability in visual assessments of intermediate-density tissue. These findings have implications for how density status changes are incorporated into patient education, risk assessment, and supplemental screening recommendations.[Table: see text]