A fully human agonistic monoclonal antibody to tumor necrosis factor-related apoptosis-inducing ligand receptor-1 (TRAIL-R1) with apoptosis promoting and potential antitumor activities. TRAIL-R1 is a cell surface receptor expressed on many malignant cell types. Mapatumumab selectively binds to and activates the TRAIL cell receptor, thereby inducing apoptosis and reducing tumor growth. or A substance being studied in the treatment of some types of cancer. It binds to a protein called TRAIL R1 on the surface of some tumor cells. This may kill the tumor cells. Mapatumumab is a type of monoclonal antibody. Also called anti-TRAIL R1-mAb and HGS-ETR1.