CCL17 and neoplasm: In addition, it has been observed that STAT-3 is an important regulator of NK cell activity; some reports have demonstrated that STAT-3 signaling in tumor cells decreases the function of neighboring NK cells by inducing in tumor cells a lower expression of NK activating ligands (MICA/B and ULBPs) and chemoattractant factors (RANTES, IP-10, CCL2, CCL9, and CCL17).