TNF and cancer: Despite such bleak scenario, it is fortunate that tumor cells displaying decrease or absence of surface membrane MHC class I molecules, invite NK cells into action, provided tumor necrosis factor (TNF) apoptosis-inducing receptor, Fas (also termed CD95 or Apo-1 or TNFRSF6) [24] and death-inducing receptors, TRAIL (TNF-related apoptosis-inducing ligand)- R1 (death receptor (DR)4 and TRAIL-R2 (DR5) [25, 26], and NK cell-activating molecules [27, 28] are displayed on the surface of the cancer cell (Fig. 5).