CD274 and pancreatic ductal adenocarcinoma: The numeration and PD-L1 expression levels of CTC were analyzed in a clinical study involving 35 patients at various advanced stages of gastrointestinal tumors including pancreatic ductal adenocarcinoma: 74% (26/35) of patients had PD-L1-positive CTC and 60% (21/35) had at least one PD-L1-high CTCs 182.