Pancreatic ductal adenocarcinoma holds unique features to form an immunosuppressive microenvironment: a narrative review

Pancreatic ductal adenocarcinoma (PDAC) is the most common type and composes about 90% of pancreatic cancer featured with high intra-tumoral heterogeneity and poor prognosis, which has been considered the least immunogenic cancer for decades. However, this characterization might be over-simplistic, and more sophisticated approaches are needed to develop effective treatment strategies. In this review, we aim to summarize studies involving PDAC immunity in different aspects to provide a multidimensional recognition and comprehensively understanding of the mechanisms underlying the tumor microenvironment (TME) of PDAC. A database search of peer-reviewed articles published in English between 2003 and 2022 in PubMed and the Web of Science was performed. Original articles and review articles relevant to the topic were selected. We emphasized the importance of investigating tumor-infiltrating lymphocytes (TILs) in pancreatic cancer, especially focusing on CD8+ T cells, along with indicating potential therapeutic strategies to turn the immune-cold PDACs into the immune-hot ones.