Primary breast diffuse large B-cell lymphoma mimicking breast carcinoma: a case report.

BACKGROUND: Primary breast lymphoma (PBL) is an exceedingly rare extranodal malignancy that frequently mimics breast carcinoma on clinical and radiological examination, posing a significant diagnostic challenge. CASE PRESENTATION: We report a case of a 39-year-old Chinese woman who presented with two palpable right breast masses. Imaging revealed suspicious lesions classified as Breast Imaging-Reporting and Data System 4A, prompting surgical excision and biopsy. Histopathological examination and immunohistochemical (IHC) analysis confirmed a diagnosis of diffuse large B-cell lymphoma, germinal center B-cell subtype. Staging by 18F-fluorodeoxyglucose positron emission tomography/computed tomography established disease as Ann Arbor stage IE, asymptomatic (stage IEA) with an International Prognostic Index score of 0. The patient was initiated on R-CHOP chemoimmunotherapy and demonstrated a favorable response after three cycles, with no evidence of recurrence. CONCLUSION: This case highlights the importance of histopathological and IHC evaluation in differentiating PBL from breast carcinoma. Early and accurate diagnosis is essential to guide appropriate treatment and optimize patient outcomes.