Supplemental breast cancer screening after negative mammography in U.S. 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 MRI within one year, respectively. Onsite availability was associated with ultrasound (odds ratio [OR]=4.35; 95%CI : 4.21-4.49) but not MRI (OR = 0.94; 95%CI : 0.85-1.04). Facility academic affiliation and for-profit status were inversely associated with supplemental ultrasound (OR = 0.53; 95%CI : 0.49-0.57 and OR = 0.83; 95%CI : 0.81-0.86, respectively) and positively associated with supplemental MRI (OR = 3.04; 95%CI : 2.86-3.46 and OR = 1.88; 95%CI : 1.66-2.12, respectively). Supplemental screening was more likely to occur after passage of state-specific density notification laws than before passage (OR = 3.56; 95%CI 3.30-3.84 and OR = 1.79; 95%CI 1.60-2.00, respectively). These results show that supplemental breast imaging utilization has been uncommon and was related to facility factors and density legislation.