A drug used to treat certain types of B-cell non-Hodgkin lymphoma. It is also used with other drugs to treat chronic lymphocytic leukemia and rheumatoid arthritis. It is being studied in the treatment of other types of cancer and other conditions. Rituxan binds to a protein called CD20, which is found on B-cells, and may kill cancer cells. It is a type of monoclonal antibody. Also called rituximab.