A b s t r a c t Of 92 patients with lymphoplasmacytic lymphoma/Waldenström macroglobulinemia (LPL/WM) treated at our institution, diffuse large B-cell lymphoma (DLBCL) also developed in 12 (13%). In 10 patients, DLBCL developed 12 to 128 months (median, 44 months) after the diagnosis of LPL/WM. Two patients had LPL/WM and DLBCL simultaneously. Clinicopathologic features at diagnosis of LPL/WM did not predict the risk of DLBCL. Onset of DLBCL was characterized by worsening constitutional

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... , profound cytopenias, extramedullary disease, and organomegaly. Immunoglobulin light chain expression was identical in both LPL/WM and DLBCL. In situ hybridization for Epstein-Barr virus (EBV) in 8 cases of DLBCL was negative. Of 11 patients with clinical follow-up information available, 8 (73%) died within 10 months of diagnosis of DLBCL. DLBCL, most likely as a result of histologic transformation, occurs in a subset of patients with LPL/WM and is associated with aggressive clinical course and poor outcome. EBV is unlikely to be involved in transformation. Hematopathology / ORIGINAL ARTICLE Am