Primary Breast Lymphoplasmacytic Lymphoma in a Young Woman: A Rare Case of Waldenström’s Disease

Primary breast lymphomas (PBLs) are rare tumors that originate in the breast without systemic disease at diagnosis. Lymphoplasmacytic lymphoma (LPL), usually associated with Waldenström's macroglobulinemia, is exceptionally uncommon in this location. We report a case of a 36-year-old woman with no significant medical history who presented with a rapidly enlarging right breast mass. Imaging revealed a suspicious right breast lesion classified as Breast Imaging Reporting and Data System (BI-RADS) Category 4. Core needle biopsy with histopathology and immunohistochemistry confirmed CD20-negative LPL, an indolent B-cell lymphoma. The patient was treated with bendamustine-based chemotherapy and corticosteroids, with marked clinical and radiological improvement. This case emphasizes the importance of considering hematologic malignancies in the differential diagnosis of breast lesions to avoid unnecessary surgical management and ensure appropriate systemic therapy.