Pancreatic ductal adenocarcinoma (PDAC) is the most common epithelial, exocrine pancreatic malignancy, accounting for more than 80 % of the malignant neoplasms of the pancreas. Although the molecular basis of pancreatic cancer is now better understood than ever before, there remains a long distance from being completely understood. In this study, we identified the differentially expressed genes (DEGs) in PDAC tissue compared with normal tissue and constructed a co-expression network by computing the pairwise correlation coefficient between the DEGs. We applied a statistical approach of MCODE to cluster genes in the coexpression network. Ten functional modules were identified in this network. Our results strongly suggest that dysregulations of immune response, homeostasis and cell adhesion may significantly contribute to the development and progression of PDAC. Results from this study will provide the groundwork for the understanding of PDAC. Future studies are needed to confirm some of the possible interactions suggested by this study.