The multi-faceted roles of prostaglandin E2 in cancer-infiltrating mononuclear phagocyte biology

Extensive research in the last two decades implemented that the inflammatory cell infiltrate, especially in solid tumors, is a major determinant for patient prognosis. Mononuclear phagocytes, i.e. monocytes/macrophages, dendritic cells and myeloid-derived suppressor cells, constitute the majority of tumor-associated immune cells. Instead of inducing anti-tumor immunity, mononuclear phagocytes are functionally subverted by tumor microenvironmental factors to support each stage of oncogenesis. Although mechanisms how tumors program their inflammatory infiltrate to support tumor development are ill-defined, few master regulators are beginning to emerge. One of them is the inflammatory eicosanoid prostaglandin E2 (PGE2), produced by tumor cells or the infiltrating immune cells. In this review we summarize the impact of PGE2 on mononuclear phagocytes in inflammation and cancer and discuss potential implications for cancer therapy.