PTGS2 and neoplasm: Both tumor-derived factors and products produced by non-tumor cells in the microenvironment, including G-CSF, GM-CSF, cytokines (e.g., IL-1β, IL-4, IL-6, interferon-γ), S100A8/A9, cyclooxygenase-2 and prostaglandin E2, indoleamine 2,3-dioxygenase, and ROIs can promote MDSC development and/or immunosuppressive activity [22], [24], [45]–[49].