The response rate of R-CHOP therapy on young patient with diffuse large B-cell lymphoma (positivity for CD20) was 83 percent. The disease was progressive , refractory and relapse about 15-25 percent. In these situations, the selective treatment regimen was chemotherapy (ICE, DHAP, ESHAP...) plus monoclonal antibody Rituximab. Some studies have recently showed that the antigen CD20 disappeared after Rituximab treatment. In the research of Nathalie A Johnson, 1.2 percent of diffuse non-Hodgkin lymphoma with positivity for CD20 has poor prognosis. At Ho Chi Minh city Blood Transfusion and Hematology Hospital, a male patient, 49 years old, diagnosed diffuse large B-cell lymphoma (positivity for CD20) in lymph nodes, bone marrow infiltration, stage IVb, refractory after 03 cycles of R-CHOP, reduced CD20 expression.