Micronodular T-cell/histiocyte-rich large B-cell lymphoma of the spleen: histology, immunophenotype, and differential diagnosis.

Occasionally, primary large B-cell lymphomas (LBLs) arising in the spleen present with a micronodular pattern involving the splenic white pulp but sparing the red pulp. Histologically, the nodules contain scattered large B cells in a background of numerous T cells and histiocytes. They can cause substantial difficulty in histologic diagnosis as the morphology can mimic reactive and inflammatory lesions as well as other lymphoid neoplasms. In this study, we examined the histology and immunophenotype of the micronodular T-cell/histiocyte-rich LBL (MTLBL) of the spleen with a view to establish the characteristics that may be helpful in diagnosis. Paraffin-embedded material from 17 cases of MTLBL was studied. Clinical features and histology were reviewed and immunohistochemistry was performed for immunoglobulins, CD20, CD79a, CD3, CD68, CD10, BCL6, BCL2, OCT-2, epithelial membrane antigen, CD30, CD138, and EBV markers. The median age of presentation was 56 years, and the most frequent presenting features were anemia and B symptoms. All cases showed a micronodular pattern of involvement. The tumor nodules comprised a mixture of numerous CD3+ T cells and CD68+ histiocytes and scattered large CD20+ B cells with immunoglobulin light chain restriction. They were positive for BCL6 and OCT2 but negative for CD10, CD138, and EBV markers. There was variable expression of epithelial membrane antigen, Bcl-2, and CD30. No follicle dendritic cell meshwork infrastructure underlying the nodules could be demonstrated by staining for CD21 or CD35 antigens. The prognosis was poor; seven of the 12 cases with follow-up were dead within 2 years. MTLBL is unique variant of T-cell/histiocyte-rich diffuse LBL, characterized by primary splenic presentation and a micronodular architecture. The main differential diagnoses include granulomatous inflammation, Hodgkin's lymphoma, follicular lymphoma, and peripheral T-cell lymphomas.