Fig. 1

Lymph node biopsy showing Richter syndrome. The lymph node architecture was effaced by a diffuse proliferation of large lymphoid cells with features of immunoblasts. A starry sky pattern and frequent mitoses were also noted. The large cells were intermixed with a numerically smaller population of small, mature-appearing lymphocytes. The large cells were positive for CD20, CD79a, BCL6, and MUM1 and negative for CD10 and CD3 by immunohistochemistry. The Ki-67 proliferation index was approximately 80%, and in situ hybridization for Epstein-Barr virus was negative. According to Hans' algorithm, these findings are consistent with diffuse large B-cell lymphoma, activated B-cell subtype, arising in a background of chronic lymphocytic leukemia/small lymphocytic lymphoma