The impact of adjunctive tomosynthesis on screening mammography outcomes in two widely diverse radiology practices.

To determine the effect of adjunctive digital breast tomosynthesis screening on dissimilar mammography practices. We compared the outcomes of breast cancer screening with digital mammography versus digital mammography combined with tomosynthesis in two independent breast imaging practices from June 1, 2015, to May 31, 2016. Institution one was a hospital-based academic practice of breast imaging specialists and institution two was a community-based practice with academic affiliation served by general radiologists. Screening mammography was linked to subsequent diagnostic imaging and pathology. Subject characteristics and performance metrics were compared via t test for continuous variables and the chi-square test for categorical variables. A two-sided z test was performed to test modality differences for assessment and pathology subtype. Of the 54 638 women, 54% (n = 29 295) were from institution one and 55% (n = 30 013) underwent digital mammography alone. Women undergoing mammography with tomosynthesis were older (60.8 years vs 56.9 years, P < .001) and had slightly less dense breast composition (P = .001). Performance metrics varied substantially between institutions. At both institutions the biopsy rate, positive predictive value of screening (PPV1 ), and invasive cancer detection rate increased significantly with adjunctive tomosynthesis. At institution one, the biopsy rate increased from 1.4% to 1.9%, the PPV1 from 6.0% to 8.2%, and the invasive cancer detection rate from 3.4 to 4.9/1000 women screened. At institution two, the respective increases were from 0.7% to 1.0%, 5.5% to 11.0%, and 2.3% to 4.1/1000. Tomosynthesis recalled asymmetry less and mass more and resulted in fewer BI-RADS 1 and 2 assessments than screening with mammography alone. Adjunctive tomosynthesis appears to have a consistent impact on breast cancer screening performance metrics despite marked variation in breast imaging practice. Combined tomosynthesis screening has a significantly higher PPV1 , leads to a greater number of biopsies, and detects more invasive cancer than screening with digital mammography.