Role of the tumor microenvironment in pancreatic cancer

Pancreatic cancer remains a highly recalcitrant disease despite the development of systemic chemotherapies. New treatment options are thus urgently required. Dense stromal formation, so-called "desmoplastic stroma," plays controversial roles in terms of pancreatic cancer growth, invasion, and metastasis. Cells such as cancer-associated fibroblasts, endothelial cells, and immune cells comprise the tumor microenvironment of pancreatic cancer. Pancreatic cancer is considered an immune-quiescent disease, but activation of immunological response in pancreatic cancer may contribute to favorable outcomes. Herein, we review the role of the tumor microenvironment in pancreatic cancer, with a focus on immunological aspects.