In pancreatic ductal adenocarcinoma, CTCs increase the expression of regulator of G-protein signaling 18 (RGS18) under the influence of platelets, and RGS18 can upregulate human leukocyte antigen-E (HLA-E) expression via the AKT-GSK3β-CREB signaling pathway. Here, RGS18 is linked to pancreatic ductal adenocarcinoma.