For example, PD-1 upregulation was recently found in NK cells from multiple myeloma, Kaposi sarcoma, and head and neck cancer patients.16,34–36 TIGIT expression on NK cells was further upregulated in tumor regions compared with peritumoral regions in colorectal tumors.10,24,37–39 CD96, CD112R, TIM-3, NKG2A, LAG-3, and IL-1R8 are other significant receptors that have been proved to be upregulated on NK cells in cancers.26,40,41. Here, PDCD1 is linked to cancer.