A drug used with the drug rituximab to treat certain types of B-cell non-Hodgkin lymphoma. It is also being studied in the treatment of other types of B-cell tumors. Yttrium Y 90 ibritumomab tiuxetan contains a monoclonal antibody that binds to a protein called CD20, which is found on B cells. It also contains a radioactive substance called yttrium Y 90, which may help kill cancer cells. Yttrium Y 90 ibritumomab tiuxetan is a type of radioimmunoconjugate. Also called IDEC-Y2B8, Y 90 ibritumomab tiuxetan, and Y 90 Zevalin. OR A radioimmunotherapeutic agent consisting of a murine monoclonal anti-CD20 antibody (ibritumomab) linked by the chelator tiuxetan to the radioisotope yttrium-90 (Y 90). Yttrium Y 90 ibritumomab tiuxetan binds to and specifically delivers beta radiation to CD20-expressing tumor cells, thereby minimizing the systemic effects of radiation. Check foractive clinical trials using this agent.