[Loss of CD20 expression following rituximab-combined chemotherapy in CD20-positive and CyclinD1-positive multiple myeloma].

Several studies have confirmed that CD20 is expressed in about 20% of multiple myeloma (MM) cases. This is closely related to a chromosomal translocation between chromosome 11 and chromosome 14, which results in the expression of CyclinD1. The use of rituximab (RIT) in the treatment of CD20-positive MM has been reported, however its effectiveness is still not well established. We encountered a case of CD20-positive/CyclinD1-positive MM; interestingly, CD20 expression could not be detected in MM cells following RIT-combined chemotherapy, while it gradually recovered when RIT therapy was discontinued. This is the first report in which the transition of CD20 expression was accurately analyzed by flow cytometry and immunohistochemical staining before, during and after RIT treatment. Consequently, this case provides insight regarding the mechanism through which CD20 expression is lost following RIT therapy for CD20-positive lymphoid neoplasm, as well as the efficacy of RIT in CD20-positive MM.