A recent study reported that CD137 (also known as 4-1BB), a surface glycoprotein belonging to the tumor-necrosis factor receptor superfamily, is upregulated on human NK cells when they encounter antibody-bound tumor cells, and that the cytotoxicity of these activated NK cells is enhanced by their exposure to an agonistic mAb against CD137, leading to improved antitumor activity in xenotransplant models of B cell lymphoma, breast, colon, and head and neck cancer [16–18]. This evidence concerns the gene TNFRSF9 and head and neck cancer.