Primary breast diffuse large B-cell lymphoma mimicking breast carcinoma: a diagnostic challenge – case report

Introduction: Primary breast lymphoma (PBL) is a rare malignancy that may clinically and radiologically mimic breast carcinoma. Accurate pathological diagnosis is essential to guide treatment and avoid unnecessary radical surgery. Presentation of case: A 47-year-old woman presented with a painless right breast mass and ipsilateral axillary lymphadenopathy. Initial core-needle histology was interpreted as grade 2 invasive ductal carcinoma, and the patient underwent right mastectomy with axillary dissection. Postoperative immunohistochemistry (IHC) showed tumor cells positive for CD20 and negative for cytokeratin and T-cell markers, consistent with primary breast diffuse large B-cell lymphoma (PB-DLBCL). The patient received six cycles of R-CHOP and remains in complete remission at a 2-year follow-up. Discussion: PBL may be morphologically indistinguishable from carcinoma on limited H&E sections. Therefore, IHC is essential to differentiate lymphoma from epithelial malignancy; when feasible, adequate preoperative sampling and targeted immunostains should be considered to prevent unnecessary mastectomy. R-CHOP chemotherapy is the mainstay of treatment for PB-DLBCL. Conclusion: Consider PBL in the differential diagnosis of breast masses. Adequate sampling and IHC are crucial to directing appropriate, non-surgical therapy.