PIWIL1 and pancreatic ductal adenocarcinoma: Previous studies have demonstrated that Piwil1 played a key role in enhancing tumor malignant behavior including proliferation [13, 15] and invasion [16], as well as the potential importance of Piwil1 expression as a marker of poor prognosis in soft-tissue sarcoma and ductal adenocarcinoma of the pancreas [17, 18].