Background For image-guided core-needle breast biopsy (CNBB), it remains unclear whether antithrombotic medication should be withheld because of hematoma risk. Purpose To determine hematoma risk after CNBB in patients receiving antithrombotic medication and to stratify risk by antithrombotic type. Materials and Methods This HIPAA-compliant retrospective study included US-, stereotactic-, or MRI-guided CNBBs performed across six academic and six private practices between April 2019 and April 2021. Patients were instructed to continue antithrombotic medications, forming two groups: antithrombotic and nonantithrombotic. Hematomas were defined as new biopsy-site masses with a diameter of 2 cm or larger on postprocedure mammograms. Hematomas were considered clinically significant if management involved an intervention other than manual compression. Patient age, type of antithrombotic medication, practice type, image guidance modality, needle gauge and type, and outcome of pathologic analysis were recorded. Multivariable logistic regression analysis was used to analyze variables associated with hematomas. Results A total of 3311 biopsies were performed in 2664 patients (median age, 60 years; IQR, 48-70 years; 2658 women). The nonantithrombotic group included 2788 biopsies, and the antithrombotic group included 523 biopsies (328 low-dose aspirin, 73 full-dose antiplatelet drugs, 51 direct oral anticoagulants, 36 warfarin, 32 daily nonsteroidal anti-inflammatory drugs, three heparin or enoxaparin). The antithrombotic group had a higher overall hematoma rate (antithrombotic group: 49 of 523 biopsies [9.4%], nonantithrombotic group: 172 of 2788 biopsies [6.2%]; P = .007), but clinically significant hematoma rates were not different (antithrombotic group: two of 523 biopsies [0.4%], nonantithrombotic group: one of 2788 biopsies [0.04%]; P = .07). At multivariable analysis, age (odds ratio [OR], 1.02; 95% CI: 1.01, 1.03; P < .001), 9-gauge or larger needles (OR, 2.1; 95% CI: 1.28, 3.3; P = .003), and full-dose antiplatelet drugs (OR, 2.5; 95% CI: 1.29, 5.0; P = .007) were associated with higher hematoma rates. US guidance (OR, 0.26; 95% CI: 0.17, 0.40; P < .001) and 10-14-gauge needles (OR, 0.53; 95% CI: 0.36, 0.79; P = .002) were predictive of no hematoma. Conclusion Because clinically significant hematomas were uncommon, withholding antithrombotic medications before core-needle breast biopsy may be unnecessary. Postbiopsy hematomas were associated with full-dose antiplatelet drugs, patient age, and 9-gauge or larger needles. No association was found with other types of antithrombotic medication. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Chang and Yoen in this issue.

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