Primary Breast Lymphoma: A Rare Presentation of Diffuse Large B-Cell Lymphoma, Germinal Center B-Cell Subtype (DLBCL-GCB).

Primary breast lymphoma (PBL) is a rare type of extranodal lymphoma, accounting for only 0.5% of all breast malignancies. Diffuse large B-cell lymphoma (DLBCL) is the most common histological subtype of PBL, with the germinal center B-cell (GCB) subtype being an exceptionally rare clinical occurrence. This report describes a rare case of primary breast lymphoma of the DLBCL-GCB subtype, presenting as a rapidly enlarging breast mass. A 50-year-old female patient presented with a palpable, painless mass in her left breast. Despite a non-suspicious mammogram (breast imaging-reporting and data system (BI-RADS) 3), the presence of hypoechoic lesions with irregular margins in the ultrasound raised concern (BI-RADS IVc), prompting further imaging. Positron emission tomography-computed tomography (PET-CT) and MRI showed multifocal disease confined to the left breast and ipsilateral axillary lymph nodes, without distant metastasis. Core needle biopsy confirmed the DLBCL-GCB subtype. The patient was treated with eight cycles of rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) chemotherapy. A mid-treatment PET-CT, performed after four cycles, demonstrated complete regression of hypermetabolic lesions in the left breast. The patient remains in remission on follow-up, suggesting a favorable early outcome. PBL poses diagnostic challenges due to its rarity and clinical overlap with more common breast malignancies. A thorough, multimodal diagnostic approach, combining imaging and histopathology, is essential to ensure accurate diagnosis. Management is primarily based on systemic chemotherapy, often complemented by radiotherapy, with treatment individualized according to disease extent and patient factors.