YAP1 and pancreatic ductal adenocarcinoma: KRAS mutation could induce LIF expression in human pancreatic ductal adenocarcinoma (PDAC) cells, and LIF inhibits the intracellular Hippo pathway and promotes tumorigenesis by facilitating YAP/TAZ-TEAD interaction and up-regulating the expression of the YAP1 target genes CNTF and ANKRAD.