CD16− CD56+ cells in peripheral blood are not cytotoxic under normal circumstances; however, when activated by several cytokines, some of them acquire CD16 expression and show up-regulated CD56 expression, and these cells produce large amounts of IFN-γ and exert strong antitumor cytotoxicity against not only MHC class I-negative but also MHC class I-positive (that is, NK-resistant) tumor cells [70]. This evidence concerns the gene NCAM1 and neoplasm.