While NK cells consistently defend against tumor cells, immunosuppressive strategies have been adopted by tumor cells to evade slaughter from NK cells, mainly through secretion of multiple cancer-associated soluble immunosuppressive molecules, including IL-10, indoleamine 2,3-dioxygenase, PGE2, and TGF-β) into the TME [149,150,151]. The gene discussed is IDO2; the disease is neoplasm.