Cytologic Findings of Primary Thyroid MALT Lymphoma With Extreme Plasma Cell Differentiation: FNA Cytology of Two Cases

We report fine-needle aspiration cytology (FNAC) obtained from two cases of mucosa-associated lymphoid tissue (MALT) lymphoma with extreme plasma cell differentiation. The patients were 61-year-old and 69-year-old Japanese women presenting with thyroid swelling. The smears contained numerous plasma cells, lymphocytes with plasma cell differentiation and scattered centrocyte-like (CCL) cells. In addition, one case demonstrated occasional atypical giant plasma cells. Occasional intranuclear inclusions (Dutcher bodies) of the plasma cells were observed in the other case. A few cytologic lymphoepithelial lesions-clusters (originating from lymphoepithelial lesions in histology) were also observed in one case. Plasma cells occupied similar to 10% in all of the lymphoid populations in FNAC specimens of Hashimoto thyroiditis, whereas, both cases demonstrated similar to 45% plasma cells and lymphocytes with plasma cell differentiation of all lymphocytes. The cytomorphologic findings of both cases were similar to those of plasmacytoma of the thyroid. However, immunohistochemical and flow; cytometry studies demonstrated that both cases were MALT lymphoma with extreme plasma cell differentiation. From a therapeutic perspective, it is important to discriminate MALT lymphoma from plasmacytoma. Diagn. Cytopathol. 2009;37:815-819. (C) 2009 Wiley-Liss, Inc.