[Loss of CD23 expression after bortezomib plus dexamethasone therapy in CCND1/IGH-positive multiple myeloma].

A 69-year-old male was referred to our hospital because of anemia, renal insufficiency, and a positive urine test for Bence-Jones protein. A bone marrow examination showed 73.7% of myeloma cells with lymphoplasmacytic morphology, the strong expressions of CD20 and CD23 by flow cytometry, and the chromosomal aberration of CCND1/IGH by FISH analysis. He was diagnosed with multiple myeloma, IgG-λ type. The initial treatment with bortezomib plus dexamethasone (BD) provided a rapid decrease in the level of IgG; however, he developed bortezomib-induced recurrent paralytic ileus accompanied by aspiration pneumonia during the second course. Interestingly, CD23 expression on myeloma cells decreased from 87.7% to 2.2% after 2 courses of BD. Negative CD23 expression was maintained following lenalidomide plus dexamethasone therapy. There are extremely few reports on CD23 expression on myeloma cells, and this is the first case report of multiple myeloma in which CD23 expression was lost after BD therapy.