CD5- and CD23-Positive Splenic Diffuse Large B-Cell Lymphoma with Very Low CD20 Expression

We report a rare primary splenic diffuse large B-cell lymphoma demonstrating CD5(+) and CD23(+) with very low CD20 expression. The only lesion was detected in the spleen, which was extremely enlarged with multiple large white-colored nodules. The lesion was characterized by a diffuse growth pattern of medium- to large-sized lymphoma cells with abundant cytoplasm. Immunohistochemical and flow cytometric study demonstrated that the lymphoma cells were negative for CD2, CD3, CD4, CD8, CD10, CD56, CD138, ALK-1, λ-light chain, and cyclin-D1, and positive for CD5, CD19, CD23, CD25, CD38, CD43, CD79a, IgM, IgD, κ-light chain, BCL2, BCL6, BOB. 1, Oct-2, Pax5, and MUM-1. CD20 was very weakly positive immunohistochemically, and negative by flow cytometric analysis. These findings resembled Richter syndrome, although chronic lymphocytic leukemia was not preexisting. Extremely poor outcome might be supposed because the effect of rituximab might be quite limited since CD20 was very weakly positive, in addition to an inferior prognosis of both CD20(-) and CD5(+) diffuse large B-cell lymphoma. Careful management is thus necessary.