PRF1 and neoplasm: NK cells are known as cytotoxic cells of the innate response and in tumors, are principal effectors of the cancer immunoediting by recognizing and destroying tumor cells directly through the exocytosis of granules with perforin and granzyme, apoptosis mediated by different death receptors (FasL, TRAIL, and TNF-α), and IFN-γ secretion [12,25,26].