Diagnostic features of primary malignant lymphomas of the thyroid with monoclonal antibodies

Primary malignant lymphomas (ML) of the thyroid are rare and their conclusive morphologic diagnosis is not always possible. The authors report diagnostic features of 11 cases of ML and one case of plasmacytoma of thyroid compared with chronic lymphocytic thyroiditis and undifferentiated carcinomas of thyroid in an immunohistochemical study using monoclonal antibodies (MoAb). The lymphoid nature of tumors could be identified in all cases with three MoAb on paraffin sections. In ML, tumor cells expressed leucocyte common antigen (Dako-LC+) with negativity for epithelial membrane antigen (Dako-EMA-) and cytokeratin (KL1-). Newer MoAb identifying B-cell (LN-1, LN-2, MB2) and T-cell-associated antigens (MT1, UCHL1) not denatured by fixation, revealed B-cell nature of tumor cells in all cases of ML. Among anti-B MoAb, LN-1 and MB2 were most consistent in their reactivity. In cryostat sections of three ML cases, the tumor cells expressed one or more B-cell-associated antigens. Plasmacytoma was negative for Dako-LC and KL1 but positive for Dako-EMA and monotypic cytoplasmic Ig.