A drug used to treat chronic lymphocytic leukemia (CLL) that has not gotten better with other chemotherapy. It is also being studied in the treatment of other types of cancer, including follicular non-Hodgkin lymphoma. Ofatumumab binds to CD20, a protein on the surface of normal B cells and most B-cell tumors. This may kill the cancer cells. It is a type of monoclonal antibody. Also called Arzerra and HuMax-CD20.