Background: Extramedullary plasmacytoma of the breast is an uncommon neoplasm, occurring either as a solitary tumor or as evidence of disseminated multiple myeloma.

Methods: Two cases of plasmacytoma of the breast were diagnosed by fine needle aspiration cytology. Aspiration smears showed a dispersed population of plasmacytoid cells with eccentric nuclei, abundant cytoplasm and the characteristic paranuclear hof.

Conclusions: The clinical, cytologic and immunophenotypic features of plasmacytoma are characteristic, and the importance of distinguishing these neoplasms from primary mammary tumors is important to avoid unnecessary surgery.