[CD20-positive plasma cell myeloma with lymphoplasmacytoid appearance mimicking low-grade B-cell lymphoma].

CD 20 positive myeloma with small lymphoplasmacytoid morphology is difficult to differentiate from mature B-cell lymphoma. A 71-year-old male was referred to our hospital because of osteolytic vertebral fractures and anemia. Urine was positive for Bence Jones protein, κ type. Bone marrow consisted of approximately 30% small lymphoplasmacytoid cells with scant cytoplasm, and these cells were positive for CD20, CD23 and CD138. FISH analysis revealed t(11;14)(CCND1/IGH). Myeloma with t(11;14) is closely associated with small lymphoplasmacytoid appearance and CD20 and CD23 expressions. The patient was diagnosed as having myeloma based on clinical and cytogenetic findings, and achieved VGPR (very good partial response) after treatment with lenalidomide.