STAT3 and pancreatic ductal adenocarcinoma: For example, M-MDSC-driven immunosuppression in pancreatic ductal carcinoma is mediated by STAT3.151 Galiellalactone, a STAT3 inhibitor, suppresses M-MDSC development and immunosuppression.152 STAT3 phosphorylation mediates the expression of Arg-1.