Since 2009, despite insufficient evidence, 24 states have enacted legislation that encourages supplemental
breast cancer screening with advanced breast imaging to all women with dense breasts. Patient advocacy
efforts that led to the legislation contend that breast density may modestly increase risk for breast cancer but
reduce the accuracy of screening mammography. Nearly 31 million women have “dense breasts”, more than
60% of whom live in states with notification legislation. Because of the potential for increased cancer detection
with tests such as ultrasound and magnetic resonance imaging (MRI), their use as supplemental screening is
expected to overcome some of the limitations of screening mammography. However, such use will also
increase false-positives and unnecessary biopsies as ultrasound and MRI have lower specificities than
mammography. Further concerns have been raised about the potential for over-treatment and overdiagnosis
from supplemental screening. The critical question is whether state-level laws requiring breast density
notification and encouraging use of supplemental screening tests will improve the detection of cancer, down-
stage these cancers when they are found, and ultimately, increase the number of deaths averted from breast
cancer. To fill this evidence gap, we will capitalize on the natural experiment formed by state-specific
legislation and use interrupted time series with comparison series to analyze data from 50 states spanning 18
years (January 1, 2001 through December 31, 2018) to rigorously assess the impact of breast density
reporting legislation on: 1) breast cancer imaging (including ultrasound, MRI, tomosynthesis) and diagnostic
workup and patient costs using claims data from a large cohort of commercially-insured women; and 2) breast
cancer detection rates using cancer registry data. Our overarching hypothesis is that density notification laws
have led to a significant increase in diagnostic resource utilization without a corresponding clinically significant
decrease in detection of late stage breast cancer. We have assembled a multidisciplinary research team with
internationally-recognized clinicians and methodologists in health policy evaluation, particularly the use of
interrupted time series and in breast density and breast cancer screening policy. This research will move the
field forward through the combination of a rigorous quasi-experiment design and two unique and
complementary datasets to address these critical and time-sensitive questions about benefits and harms from
density notification legislation. Our research can inform the ongoing policy debates in additional states and at
the federal level. Further, by examining diagnostic burden and financial cost, we will provide women and their
clinicians with information essential for deciding whether to undergo supplemental screening.
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