Nowadays,resistance to rituximab has become a major issue in clinical practice.And loss of CD20 may contribute to it.Here we presented a case of loss of CD20 expression in relapsed diffuse large B cell lymphoma treated with rituximab and discuss the incidence,mechanism,influence factors,specific markers,prognosis and treatment of this disease.These results suggested that a post-relapse biopsy after rituximab treatment should be performed.CD79a and Pax-5 should be used as the first-line B lineage-specific markers for these patients.Though mechanisms of CD20 decrement are not fully elucidated,the down-regulation of CD20 mRNA is the most probable hypothesis.Recently various new agents are developed,but the prognosis is still poor.Further studies for new treatments are needed.
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