MICROVILLOUS LYMPHOMAS ARE B-CELL NEOPLASMS THAT FREQUENTLY EXPRESS CD56

Microvillous lymphomas (MVLs) are rare, poorly defined, large transfor med cell lymphomas characterized by a cohesive sinus growth pattern an d ultrastructural cytoplasmic processes. Most MVLs express B-cell anti gens and have been compared ultrastructurally to transformed follicula r center cells and follicular dendritic cells. For additional definiti on of the immunophenotype of these unusual B-cell lymphomas, we evalua ted eight cases of MVL for B-cell-associated antigens (CD21, CD35, CDw 75, DBA.44, bcl-2) using paraffin immunoperoxidase. CD56, the neural c ell adhesion molecule, was tested because of the unusual, cohesive, si nus pattern of tumor cell growth seen in MVL. Molecular analysis for i mmunoglobulin heavy chain and bcl-2 gene rearrangements was performed to confirm B-cell clonality and to evaluate cases for possible follicu lar origin. All of the cases were marked as B cells (CD20 positive), a nd the clonal nature confirmed by immunoperoxidase in five cases (63%) of eight and polymerase chain reaction for immunoglobulin heavy chain in seven cases (88%) of eight. CDw75 staining was present in six case s and CD74 in seven. DBA.44 and CD21 and CD35 were negative in all of the cases, and four cases (50%) of eight expressed CD56, bcl-2 protein expression was seen in seven of eight cases; bcl-2 gene rearrangement was present in one case (33%) of three studied. In conclusion, MVLs a re B-cell lymphomas demonstrating clonal immunoglobulin heavy chain ge ne rearrangement, The neoplastic cells express CDw75 and bcl-2 protein . The presence of bcl-2 rearrangements in a limited number of cases im plies that at least some MVLs have a follicular origin. Fifty percent of MVLs express CD56, suggesting a role for adhesion molecules in the distribution of this lymphoma.