PRF1 and cancer: The described mechanisms allow NK cells to recognize tumor cells and mediate tumor cell killing either through: (1) The release of cytotoxic granules containing granzyme and perforin, which cause cancer cell lysis [44,45]; or, (2) the secretion of cytokines (e.g., IFN-γ and TNF-α) and chemokines (e.g., chemokine C-C motif ligand 3 (CCL3), CCL4 and CCL5) into the extracellular microenvironment, which trigger tumor cell apoptosis and can shape the immune response of other cells of the immune system [55,61].