Dense breast tissue is a common finding that decreases the sensitivity of mammography in detecting cancer. Many states have recently enacted dense breast notification (DBN) laws to provide patients with information to help them make better-informed decisions about their health. To test whether DBN legislation affected the probability of screening mammography follow-up by ultrasound and magnetic resonance imaging (MRI), we examined the proportion of times screening mammography was followed by ultrasound or MRI for a series of months pre- and post-legislation. The subjects were women aged 40 to 64 years, covered by private health insurance, undergoing screening mammography from 2007 to 2014. Except for Hawaii, Maryland, and New York, DBN legislation significantly increased the probability of ultrasound follow-up in all states that implemented DBN legislation before December 2014. It also increased the probability of MRI follow-up in California, North Carolina, Pennsylvania, and Texas. The financial and access consequences merit further study.
Keywords: breast magnetic resonance imaging; breast ultrasound; dense breast tissue; follow-up; screening mammography; state law.