For example, platelet-derived growth factor DD (PDGF-DD) has been shown to be released by many types of tumors and to activate the NK cells’ receptor NKp44, stimulating the secretion of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α) and chemokines to trigger tumor cell–cycle arrest [56]. This evidence concerns the gene IFNG and neoplasm.