Longitudinal Mammographic Breast Density Changes and Associated Factors in Older Korean Women.

Purpose To evaluate breast density changing trajectories in women age 60 years or older and identify their associated factors. Materials and Methods Data were obtained from the Korean National Health Insurance Service Database, which includes six biennial mammography screenings from January 2009 to December 2020. Women age 60 years or older who participated in screenings in 2009-2010 and 2019-2020 and at least two screenings in between were included. Breast density was classified using the Breast Imaging Reporting and Data System (BI-RADS). Group-based trajectory modeling was used to identify patterns of breast density changes across the six screening cycles. Logistic regression was used to examine breast cancer risk factors associated with the increasing or decreasing breast density trajectories. Results Among 674 993 women (mean age, 65.0 years ± 4.3 [SD]; 51% BI-RADS 1 at baseline), five distinct breast density change trajectories were identified: persistent fatty (20.5%), persistent BI-RADS 2 (36.1%), and persistent BI-RADS 3 (15.4%). Group 2 (17.2%) showed increased density, and group 3 (10.8%) demonstrated decreased density. Several breast cancer risk factors were associated with the breast density trajectories. For example, older women (adjusted odds ratio, 0.98; 95% CI: 0.97, 0.98; P < .001) and women with a higher baseline body mass index and a greater increase in body mass index over time were less likely to have increased breast density. Conclusion Five distinct breast density change trajectories were identified among Korean women who were age 60 years or older. Women with initially low breast density and more breast cancer risk factors were more likely to show increasing trajectory, whereas those with initially high density and fewer risk factors tended to show decreasing density. Keywords: Breast Density, Breast Density Change, Older Women, Reproductive Factors, Breast Cancer © RSNA, 2026.