OBJECTIVE. The purpose of this study was to evaluate the frequency and cancer yield of BI-RADS category 3 lesions in baseline versus nonbaseline (those with at least one prior) MRI screening examinations. MATERIALS AND METHODS. Consecutive MRI screening examinations performed from 2011 through 2015 were reviewed. Pearson and Wilcoxon tests were used to examine differences in age, breast density, screening indication, background parenchymal enhancement, and cancer yield between baseline and nonbaseline MRI BI-RADS category 3 assessments. Multivariate logistic regression models based on generalized estimating equations were used to assess the odds of receiving a BI-RADS 3 assessment as a function of the variables. RESULTS. Of 6672 MRI screening examinations of 3214 patients, 202 examinations (3%) were assessed BI-RADS category 3. Among baseline examinations, 8% (82/983) were assessed BI-RADS 3, compared with 2% (120/5689) of nonbaseline examinations (p < 0.001). Among the total BI-RADS 3 examinations, 6% (13/202) yielded malignancy of the lesion that had been assessed BI-RADS 3; 12 of 13 cancers were stage 0 or I at diagnosis. The cancer yield of BI-RADS 3 at baseline examinations was 2% (2/82), compared with 9% (11/120) for nonbaseline examinations (p = 0.056). Ten of 13 examinations were upgraded at or before 6-month follow-up MRI. CONCLUSION. Baseline screening breast MRI examinations are associated with a significantly higher rate of BI-RADS category 3 assessments than are nonbaseline examinations. Most cancers diagnosed at follow-up of BI-RADS 3 lesions are in an early stage and are diagnosed at or before the 6-month follow-up examination. When used judiciously, short-interval follow-up MRI is an appropriate method for identifying early-stage breast cancer while avoiding unnecessary biopsies with benign findings.

Sarah F. Mercaldo

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