Platelets can transfer high levels of platelet-derived normal major histocompatibility complex-1 to tumor cells with low or absent expression of MCH-1, and induce the release of soluble NKG2D ligand from the cancer cells, interfering with the recognition of cancer cells by natural killer (NK) cells, thus impairing cytotoxicity and IFN-γ production. Here, KLRK1 is linked to cancer.