A case of plasmacytoma of the breast mimicking an inflammatory carcinoma

A 42-year-old woman presented to our institution with asymptomatic swelling of the left breast for the previous 6 months along with pathologic fractures in the right humerus and the left femur for the past 2 months. Radiology revealed multiple lytic lesions throughout the skeletal system. The breast swelling was approximately 6 cm x 6 cm. The swelling was cystic-to-firm in consistency, with ill-defined margins. The skin overlying the swelling was red and had a peau d'orange appearance. There was no nipple discharge or lymphadenopathy. A differential diagnosis of breast carcinoma with multiple bone secondaries, carcinoma of unknown primary origin with breast abscess, or breast secondary or a plasmacytoma with multiple myeloma was made. Fine-needle aspiration cytology revealed sheets of immature and mature plasma cells, suggesting that it was a plasmacytoma.