Fine-needle aspiration cytology and immunocytochemistry of soft-tissue extramedullary plasma-cell neoplasms.

This study presents 19 patients with extramedullary plasma-cell tumors diagnosed by fine-needle aspiration (FNA) cytology together with immunocytochemistry. Eight patients had primary extramedullary plasmacytoma, while 11 patients had tumors secondary to myeloma. The most common localization was soft tissue (9 cases), followed by lymph nodes (5), scalp (3), and oral and nasal mucosa (2). All FNA smears were cellular, and 12 cases showed dissociated monomorphic plasma cells. Seven cases showed a dominance of immature bare nuclei, which made then difficult to diagnose conclusively using cytomorphology only. Immunocytochemistry demonstrated monoclonal expression of light immunoglobulin chains in all cases which, together with demonstration of CD 38 positivity and cytomorphology, allowed a conclusive diagnosis of plasmacytoma.