A drug used to treat certain types of B-cell non-Hodgkin lymphoma. It is also being studied in the treatment of other types of cancer. Ibritumomab tiuxetan contains a monoclonal antibody that binds to a protein called CD20, which is found on B cells and some types of lymphoma cells. It also contains the compound tiuxetan, which allows certain radioactive substances to be attached to the monoclonal antibody. This may help kill cancer cells. Ibritumomab tiuxetan is a type of monoclonal antibody and a type of immunoconjugate. Also called Zevalin.