KLRK1 and cancer: From a clinical perspective, numerous studies have shown a positive correlation between soluble MICA levels in the serum of cancer patients and their poor prognosis, indicating that it is an independent prognosis predictor and promising therapeutic target in cancer patients [14, 36–38].The shed NKG2D ligands, such as the soluble MICA and MICB, can engage NKG2D on NK cells, resulting in systemic NK cell dysfunction [39, 40].