Rarity to Remission: Complete Response of Primary Breast Diffuse Large B-Cell Lymphoma With Chemoimmunotherapy.

Primary Non-Hodgkin's lymphoma of the breast is rare, accounting for < 0.5% of breast cancers and ~2% of extranodal lymphomas. It often presents as a painless lump, mimicking carcinoma and complicating diagnosis. Case PresentationWe report a 65-year-old post-menopausal, hypertensive, and diabetic woman with a gradually enlarging left breast mass. Imaging revealed a suspicious lesion. Core biopsy suggested poorly differentiated carcinoma, but immunohistochemistry confirmed diffuse large B-cell lymphoma (DLBCL), activated B-cell subtype, with high Ki-67 (~90%). PET/CT showed localized disease. She received six cycles of CHOP chemotherapy, with rituximab added from the second cycle. Treatment was well tolerated. Follow-up PET/CT and biopsy demonstrated complete metabolic and pathological remission. ConclusionPrimary breast DLBCL is rare and easily misdiagnosed as carcinoma. Immunohistochemistry is therefore crucial for correct diagnosis. R-CHOP chemoimmunotherapy is the cornerstone of treatment.