Background Combined digital mammography (DM) and digital breast tomosynthesis (DBT) (hereafter, DM plus DBT) has increased cancer detection rates when compared with those achieved with DM-only screening. However, there is limited literature on DBT as an adjunct to mammography in the staging of known breast cancers. Purpose To compare the diagnostic accuracy of DM alone with that of DM plus DBT in the identification of additional ipsilateral and contralateral lesions in women with newly diagnosed breast cancer. Materials and Methods This prospective study ( https://clinicaltrials.gov , NCT01881880) included 166 women with breast cancer (mean age, 59.5 years ± 11; age range, 40-87 years) and used the aforementioned techniques, with breast MRI and pathologic verification of all suspected lesions as the reference standards. Four radiologists independently reviewed the DM and DM plus DBT images using the American College of Radiology Breast Imaging Reporting and Data Systems criteria for diagnosis of index lesions and presence of additional disease. Sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) obtained for DM and DM plus DBT were compared by using the McNemar test. Results Twenty-four women (14%) exhibited multifocal lesions; 20 (12%), multicentric lesions; 39 (23%), additional ipsilateral lesions; and 18 (11%), bilateral lesions. The sensitivities were higher for DM plus DBT than for DM in the diagnosis of multicentric (51% [41 of 80] vs 37% [30 of 80], P = .002) and additional ipsilateral (52% [81 of 156] vs 44% [69 of 156], P = .007) lesions. The AUC was larger for DM plus DBT than for DM (0.74 vs 0.67, P = .02) in the diagnosis of bilateral breast cancer. No significant differences in specificity were noted. The added diagnostic value of DBT was limited to the group of women with nondense breasts: For diagnosis of ipsilateral lesions, AUC of DM plus DBT versus DM was 0.74 versus 0.70 (P = .04). For diagnosis of contralateral lesions, AUC of DM plus DBT verus DM was 0.76 versus 0.68 (P = .02). Conclusion The combination of digital mammography with digital breast tomosynthesis improves diagnostic accuracy for additional ipsilateral and contralateral breast cancer in women with nondense breasts. © RSNA, 2019 See also the editorial by Moy in this issue.

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