Many cell types — including tumor cells, endothelial cells, fibroblasts, macrophages, and myeloid-derived suppressor cells (MDSCs) — express COX-2 and mPGES-1, both of which can be induced by growth factors, cytokines, and hypoxia to promote the synthesis and release of PGE2 (11). This evidence concerns the gene PTGS2 and neoplasm.