SIRT1 and pancreatic ductal adenocarcinoma: For example, in pancreatic ductal adenocarcinoma, miR-221 was identified as a prognostic marker for poor outcomes [21]; in lens epithelia cells, it was reported that miR-221 could promote apoptosis [22]; in airway epithelial cell, publications also demonstrated that miR-221 could promote apoptosis and inhibit proliferation via downregulating SIRT1 [23].