PRF1 and neoplasm: NK cells can kill tumor cells by releasing perforins and granzyme B, which induce necrotic or apoptotic cell death, and via the secretion of different antitumor cytokines, such as IL-10, IL-5, IL-13, granulocyte–macrophage colony-stimulating factor, IFN-γ, and TNF-α, which help to re-modulate the immunosuppressive environment present at the tumor site [64,65].