Moreover, recent studies have reported that NK cells have the ability to regulate tumor growth by sensing specific growth factors; for example, platelet-derived growth factor (PDGF) produced in many tumors and its receptor-β (PDGFRβ) signaling can enhance IL-15-mediated NK cell survival, and PDGF-DD engagement of NKp44 triggers NK cell secretion of IFN-γ and TNF-α resulting in the arrest of tumor cell growth [7,8]. This evidence concerns the gene PPIB and neoplasm.