Supplemental breast cancer screening after negative mammography in US women with dense breasts.

The extent and determinants of supplemental screening among women with dense breasts are unclear. We evaluated a retrospective cohort of 498 855 women aged 40-74 years with heterogeneously or extremely dense breasts who obtained 1 176 251 negative screening mammography examinations during 2011-2019 in the United States. Overall, 2.8% and 0.3% of mammograms had supplemental ultrasound or magnetic resonance imaging (MRI) within 1 year, respectively. Onsite availability was associated with ultrasound (odds ratio [OR] = 4.35, 95% confidence interval [CI] = 4.21 to 4.49) but not MRI (OR = 0.94, 95% CI = 0.85 to 1.04). Facility academic affiliation and for-profit status were inversely associated with supplemental ultrasound (OR = 0.53, 95% CI = 0.49 to 0.57, and OR = 0.83, 95% CI = 0.81 to 0.86, respectively) and positively associated with supplemental MRI (OR = 3.04, 95% CI = 2.86 to 3.46, and OR = 1.88, 95% CI = 1.66 to 2.12, respectively). Supplemental screening was more likely to occur after passage of state-specific density notification laws than before passage (OR = 3.56, 95% CI = 3.30 to 3.84, and OR = 1.79, 95% CI = 1.60 to 2.00, respectively). These results show that supplemental breast imaging utilization has been uncommon and was related to facility factors and density legislation.