Comparison of false positive rates for screening breast magnetic resonance imaging (MRI) in high risk women performed on stacked versus alternating schedules

PURPOSE Breast MRI added to mammography increases screening sensitivity for high-risk women but false-positive (FP) rates are higher and the optimal screening schedule for coordination with mammography is unclear. We compare rates of FP MRI when studies were performed on two different schedules. PATIENTS AND METHODS High-risk women at the University of Vermont who had at least 1 MRI and 1 mammogram performed within one year between 2004-2012 were eligible for inclusion in this study. Screening was considered stacked if both studies were performed within 90 days and alternating if studies were 4-8 months apart. False positive was defined in one of three ways. RESULTS 137 women had screening which met inclusion criteria and 371 MRIs were reviewed. The FP rates were similar for the two schedules when considering BI-RAD 4, 5, 0 or biopsy as a positive test. FP rates were significantly higher for the stacked schedule (18.2 vs. 10.2%, p = 0.026) when considering BI-RADS 3-4-5-0 as positive test, due to the elevated rate of BI-RADS 3 assessments among stacked exams. CONCLUSION False positive rates differ based on the type of exam (baseline or subsequent) and definition of positive but do not differ based on imaging schedule (stacked or alternating); suggesting that women and their providers may choose the imaging schedule they prefer. This is significant as a randomized clinical trial comparing the two schedules is not likely to be performed, given the high cost and large number of women needed for such a study.