A combination of drugs used to treat certain types of B-cell non-Hodgkin lymphoma. It is also being studied in the treatment of other types of cancer. Bexxar is made up of a monoclonal antibody called tositumomab and a form of tositumomab that is linked to a radioactive substance called iodine I 131. It is a type of radioimmunoconjugate. Also called Bexxar regimen and tositumomab and iodine I 131 tositumomab.