Objectives: Hematological malignancies of the breast share a presentation similar to primary breast carcinomas but differ substantially in therapeutic approach and clinical outcomes. In this study, we investigate the frequency of hematological malignancies, their relative primary and secondary occurrences, and further characterize the distinct histopathologies of these malignancies with a special focus on lymphomas. To our knowledge this is one of the largest and most comprehensive studies of breast hematologic malignancies. Methods: We conducted a retrospective review of our institution's pathology database for hematologic neoplasms diagnosed in breast tissue during a period of 22 years (1992-2014). Clinical characteristics, patient history, histologic subtype, and patient outcomes were analyzed. Results:We identified 52 cases; 46 lymphomas, 4 plasmacytomas, and 2 myeloid sarcomas. The lymphoma cases were 15 diffuse large B-cell lymphomas (DLBCLs), 14 follicular lymphomas (FLs), 8 marginal zone lymphomas (MZLs), 2 anaplastic large T-cell lymphomas, 2 peripheral T-cell lymphomas-not otherwise specified, 1 each of small lymphocytic lymphoma, Burkitt lymphoma, mantle cell lymphoma, B-cell lymphoblastic lymphoma, and T-cell lymphoblastic lymphoma. In total, 30 cases were primary and 22 cases were secondary to the breast. Primary lymphomas accounted for 60% of lymphomas. Most FLs and almost all MZLs were primary. Conclusions: Primary hematological malignancies of the breast are more common than secondary: 58 % versus 42%. This finding is more evident in lymphomas: 63% versus 37%. The most common hematological malignancy in our study was DLBCL, followed by FL and MZL. Most FLs and almost all MZLs were primary. At the same time, the percentage of primary DLBCLs in our study is lower than the percentage reported in previous studies. We suggest that this could be the result of transformation from low-grade lymphomas. Although rare, hematological malignancies of the breast warrant a higher level of clinical suspicion as they present similarly to breast carcinomas but require a substantially different therapeutic approach.