Extramedullary plasmacytoma - A form of marginal zone cell lymphoma?

Extramedullary plasmacytoma (EMP), solitary plasmacytoma of bone, and multi ple myeloma are related neoplasms, but EMP is clearly a distinct entity. Mo reover; there are histologic and clinical similarities between EMP and marg inal zone B-cell lymphomas (MZLs) displaying extensive plasma cell differen tiation, suggesting a possible histogenetic relationship. The histologic an d clinical features of 5 EMPs with extensive plasma cell differentiation we re histologically reviewed for features of MZL. The previously diagnosed MZ Ls, mucosa-associated lymphoid tissue (MALT) type, of 2 patients also were reviewed All patients were women aged 48 to 79 years. The EMPs originated i n the parotid gland, lymph nodes, dura, or small bowel. The initial tumors diagnosed as MALT-type MZL were located in the lung and small bowel. All pa tients were treated with resection, with or without irradiation therapy. On e patient also received systemic chemotherapy. All patients are alive with no evidence of disease. All tumors contained large numbers of plasma cells, constituting between 55% and 90% of the lymphoid cells. Centrocyte-like ce lls and monocytoid B cells each represented 0% to 25% of the infiltrate. Ly mphoepithelial lesions were observed in all of the tumors in sites where ep ithelium was present Reactive follicles were found in all of the tumors. EM Ps may represent MZLs that have undergone apr extensive degree of plasmacyt ic differentiation.