CD27 and pancreatic ductal adenocarcinoma: A specific subset of infiltrating B cells are strong prognostic factors in various cancers context, such as CD20+ CD27− IgM+ group and CD20+ CD27− IgM− group in hepatocellular carcinoma(HCC), IgG4+ in pancreatic ductal adenocarcinoma and CD20+ in melanoma and some other cancers [56–59].