A Rare Case of Diffuse Large B Cell Lymphoma Co-occurring with Small Lymphocytic Leukemia: De Novo Process or Richter’s Syndrome?

Abstract Introduction/Objective Diffuse large B-cell lymphoma (DLBCL) is the most prevalent subtype of lymphoma and can arise either de novo or through transformation from indolent lymphomas, such as Chronic Lymphocytic Leukemia (CLL), known as Richter syndrome (RS). DLBCL derived from RS tends to exhibit more aggressive behavior compared to de novo DLBCL. Methods/Case Report We present a case of a 57-year-old female with no significant medical history, who initially presented with antibiotic and prednisone-resistant sinusitis, progressing to bilateral neck pain and eye congestion. Computed tomography (CT) imaging revealed a 3 cm mass in the right nasal cavity extending to the right maxillary sinus and medial right orbit. Histopathological examination showed diffuse sheets of intermediate to large cells with irregular nuclear contours, dispersed chromatin, variably conspicuous nucleoli, and moderate cytoplasm. Additionally, scattered foci of monotonous, atypical lymphoid cells with lower grade morphology, including small size and condensed chromatin, were also present. Immunohistochemical analysis revealed differential staining patterns between the two cell populations. The larger atypical cells expressed CD20, PAX5, CD10, BCL-6, MUM1, BCL-2, MYC, CD19 (dim), and exhibited a high Ki-67 proliferation index (>80%). In contrast, the smaller atypical cells were positive for CD5, CD19, CD20, PAX5, BCL-2, and CD23 (subset), with a lower Ki-67 proliferation index (<5%). Flow cytometry analysis of tissue samples revealed two distinct clones: Surface Kappa-restricted CD19 dim B cells (38.9%) with CD5- CD10 dim CD20+ and surface Lambda-restricted CD19+ B cells (58.7%) with CD5+ CD10- CD20+. FISH analysis revealed no gene rearrangements. The final diagnosis was Diffuse large B-cell lymphoma, germinal center B- cell phenotype, with aggressive features and focal involvement by small lymphocytic lymphoma/chronic lymphocytic leukemia. Results (if a Case Study enter NA) NA Conclusion The relationship between the large B-cell lymphoma and SLL/CLL remains uncertain; however, given the different immunophenotype and light chain expression observed by flow cytometry, they are likely to represent separate processes.