Apoptosis, or programmed cell death, occurs during normal cellular differentiation and development of multicellular organisms. Apoptosis is induced by certain cytokines including TNF and Fas ligand (FasL) of the TNF family through their death domain containing receptors, TNFR1 and Fas (also known as CD95 or Apo-1). Recently, Pitti et al., 1998 have identified a molecule that can bind to FasL and block its binding to Fas (1). This molecule called, decoy receptor 3 (DcR3), is generally amplified in a number of lung and colon carcinomas suggesting that certain tumors may escape FasL-dependent cell death by expressing a decoy receptor that blocks FasL (1,2). An identical molecule was isolated by Yu et al, 1999 that also binds to FasL and another cellular ligand, LIGHT (herpes virus entry mediator (HVEM)-L) (3,4). It has been shown that LIGHT induces apoptosis of various tumor cells that express both lymphotoxinb receptor and HVEM/TR2 receptors. DcR3/TR6 is constitutively expressed in lung tissue, tumor cells and in endothelial cells (1,3). Like other members of TNFR superfamily, DcR1, DcR2 and OPG, DcR3/TR6 may act as an inhibitor of signaling through TNF family members, FasL and LIGHT. However, unlike DcR1 and DcR2, which are membrane-associated proteins, DcR3 is directly secreted into the extracellular space.