TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily. TRAIL binds to 2 death receptors: DR4 (TRAIL-R1) and DR5 (TRAIL-R2). Death receptors possess a cytoplasmic death domain and have been the focus of developing proapoptotic agonists due to their selectivity for malignant cells vs. normal, healthy cells.