HOTTIP and pancreatic ductal adenocarcinoma: PC: pancreatic cancer, MLR: multiple logistic regression, AUC: area under the ROC curve, PDAC: pancreatic ductal adenocarcinoma, lncRNAs: long non-coding RNAs, HOTAIR: HOX transcript antisense RNA, HOTTIP: HOXA distal transcript antisense RNA, MALAT1: metastasis-associated lung adenocarcinoma transcript 1, PVT1: plasmacytoma variant translocation 1.