CTSE and pancreatic ductal adenocarcinoma: CTSE has been recognized as a promising prognostic biomarker for multiple cancers, such as pancreatic ductal adenocarcinoma (PDAC) [25, 26], gastric [27], esophageal [28], bladder [29, 30], cholangiocarcinoma [31], rectal cancer [32], and breast cancer [33].