• Loren Saulsberry, Lydia E Pace, and Nancy L Keating.
• Department of Public Health Sciences, The University of Chicago, Chicago, IL, USA.
• J Gen Intern Med. 2019 Aug 1; 34 (8): 1441-1451.

BackgroundDense breast tissue increases breast cancer risk and lowers mammography sensitivity, but the value of supplemental imaging for dense breasts remains uncertain. Since 2009, 37 states and Washington DC have passed legislation requiring patient notification about breast density.ObjectiveExamine the effects of state breast density notification laws on use of supplemental breast imaging and breast biopsies.DesignDifference-in-differences analysis of supplemental imaging and biopsies before and after notification laws in 12 states enacting breast density notification laws from 2009 to 2014 and 12 matched control states. Supplemental imaging/biopsy within 6 months following an index mammogram were evaluated during four time periods related to legislation: (1) 6 months before, (2) 0-6 months after, (3) 6-12 months after, and (4) 12-18 months after.ParticipantsWomen ages 40-64 years receiving an initial mammogram in a state that passed a breast density notification law or a control state.InterventionMandatory breast density notification following an index mammogram.Main MeasuresUse of breast biopsies and supplemental breast imaging (breast ultrasound, tomosynthesis, magnetic resonance imaging, scintimammography, and thermography), overall and by specific test.Key ResultsSupplemental breast imaging and biopsy increased modestly in states with notification laws and changed minimally in control states. Adjusted rates of supplemental imaging and biopsy within 6 months of mammography before legislation were 8.5% and 3.1%, respectively. Compared with pre-legislation in intervention and control states, legislation was associated with adjusted difference-in-differences estimates of + 1.3% (p < 0.0001) and + 0.4% (p < 0.0001) for supplemental imaging and biopsies, respectively, in the 6-12 months after the law and difference-in-differences estimates of + 3.3% (p < 0.0001) and + 0.8% (p < 0.0001) for supplemental imaging and biopsies, respectively, 12-18 months after the law.ConclusionsAs breast density notification laws are considered, policymakers and clinicians should expect increases in breast imaging/biopsies. Additional research is needed on these laws' effects on cost and patient outcomes.

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