CD226 and neoplasm: The activity of NK cells is triggered by engaging activating (e.g., natural killer group 2D (NKG2D), DNAX accessory molecule-1 (DNAM1), natural killer protein 30 (NKp30), natural cytotoxicity triggering receptor 1(NCR1), etc.)or inhibitory receptors (e.g., natural killer group 2A (NKG2A), killer cell immunoglobulin-like receptor, two Ig domains and long cytoplasmic tail 1-3 (KIR2DL1-3), T cell immunoreceptor with Ig and ITIM domains (TIGIT), etc.)on the NK cell surface by specific ligands expressed on tumor cells.