Identifying Women With Dense Breasts at High Risk for Interval Cancer A Cohort Study

Background: Twenty-one states have laws requiring that women be notified if they have dense breasts and that they be advised to discuss supplemental imaging with their provider. Objective: To better direct discussions of supplemental imaging by determining which combinations of breast cancer risk and Breast Imaging Reporting and Data System (BI-RADS) breast density categories are associated with high interval cancer rates. Design: Prospective cohort. Setting: Breast Cancer Surveillance Consortium (BCSC) breast imaging facilities. Patients: 365 426 women aged 40 to 74 years who had 831 455 digital screening mammography examinations. Measurements: BI-RADS breast density, BCSC 5-year breast cancer risk, and interval cancer rate (invasive cancer <= 12 months after a normal mammography result) per 1000 mammography examinations. High interval cancer rate was defined as more than 1 case per 1000 examinations. Results: High interval cancer rates were observed for women with 5-year risk of 1.67% or greater and extremely dense breasts or 5-year risk of 2.50% or greater and heterogeneously dense breasts (24% of all women with dense breasts). The interval rate of advanced-stage disease was highest (> 0.4 case per 1000 examinations) among women with 5-year risk of 2.50% or greater and heterogeneously or extremely dense breasts (21% of all women with dense breasts). Five-year risk was low to average (0% to 1.66%) for 51.0% of women with heterogeneously dense breasts and 52.5% with extremely dense breasts, with interval cancer rates of 0.58 to 0.63 and 0.72 to 0.89 case per 1000 examinations, respectively. Limitation: The benefit of supplemental imaging was not assessed. Conclusion: Breast density should not be the sole criterion for deciding whether supplemental imaging is justified because not all women with dense breasts have high interval cancer rates. BCSC 5-year risk combined with BI-RADS breast density can identify women at high risk for interval cancer to inform patientprovider discussions about alternative screening strategies.