PRF1 and neoplasm: The anti-tumor mechanisms of NK cells include (1) releasing perforin (PFP) and granzyme B (Gzm-B) for target cell apoptosis; (2) regulating the death receptors FASL and TRAIL for apoptosis; and (3) secreting effector cytokines, such as IFN-γ, TNF-α, IL-5, IL-13 and G-CSF.