Primary Breast Diffuse Large B-Cell Lymphoma in a Young Lactating Mother Initially Treated as Breast Abscess: A Case Report

Background: Primary breast lymphoma (PBL) is a rare extranodal manifestation of non-Hodgkin’s lymphoma, accounting for 0.4–0.5% of breast malignancies. It often mimics benign conditions like mastitis or abscess, a diagnostic pitfall heightened in lactating women due to physiological breast changes. Case Presentation: We report the case of an 18-year-old lactating woman with a six-month history of a progressively enlarging left breast mass, initially treated as an abscess with incision and drainage without improvement. Examination revealed a large left breast mass (15x14 cm) with matted axillary and supraclavicular lymphadenopathy. Contrast-enhanced CT showed a 10x9x9 cm necrotic, infiltrative mass. Ultrasound-guided tru-cut biopsy and immunohistochemistry confirmed Diffuse Large B-Cell Lymphoma (DLBCL), Activated B-Cell (ABC) subtype with a double-expressor phenotype (C-MYC and BCL-2 positive). The patient received six cycles of R-CHOP chemotherapy followed by oncoplastic surgery (modified Benelli technique) for a residual lump, achieving a complete pathological response (ypT0). Conclusion: This case underscores that a non-resolving breast abscess in a lactating woman warrants investigation for primary breast lymphoma. Early diagnosis via core biopsy and timely systemic chemotherapy are crucial for managing this aggressive malignancy, with surgery reserved for residual disease.