CD20 is a B-lymphocyte surface membrane protein, and CD20 positivity means that B cells express the surface differentiation antigen 20. CD20 is a phosphorylated protein molecule, and as a B-lymphocyte surface membrane protein, it is expressed only in pre-B-lymphocytes, immature, mature, and activated B-lymphocytes, and is lacking in plasma cells, lymphoid pluripotent stem cells, and other tissues, and there is no free CD20 present in human serum. Clinically, CD20 positivity is common in diffuse large b-cell lymphoma, follicular lymphoma, and small cell lymphoma, condyloma, and other B-cell lymphomas, for example. Rituximab, an antibody against CD20, is used to treat CD20-expressing b-lymphoblastomas. When CD20 is positive, you should go to a regular hospital and be treated under a doctor’s supervision.