CD20 is a molecular marker present on the surface of B lymphocytes, which is found only in B-lineage lymphocytes. In clinical practice, CD20 is not found in any other type of lymphocytes. Because of this, a monoclonal antibody to CD20, or melphalan, was invented in the clinic. This drug is administered through human CD20 and then injected into mice to stimulate them to produce anti-CD20 antibodies. Also in many patients with lymphoma, such as diffuse large B-cell lymphoma, follicular lymphoma, set cell lymphoma, and small cell type lymphoma, the lymphoma cells contain large amounts of CD20, which can be treated with CD20 monoclonal antibody for molecular targeting, and the CD20 monoclonal antibody can then bind to the CD20 receptor and cause the destruction of the lymphoma cells, thus achieving the goal of treating lymphoma.