TNFRSF11B and neoplasm: TRAIL is physiologically expressed by the innate immune system for anti-tumor surveillance [5], and can bind to five receptors: two death receptors TRAIL-R1 (Death Receptor 4: DR4) and TRAIL-R2 (DR5), and three decoy receptors that do not transmit the death signal but could confer resistance toward TRAIL-induced apoptosis: TRAIL-R3 (Decoy Receptor 1: DcR1), TRAIL-R4 (DcR2) and the soluble osteoprotegerin (OPG).