PTGS2 and colorectal cancer: ω-6 PUFAs in the microenvironment can upregulate PGE2 production in colorectal cancer cells and promote the transformation of myeloid-inhibiting cells (MDSC) into M2 macrophages (23); hypoxia-inducible factor-1α (HIF-1α) secreted by M2 macrophages promotes tumor invasion and metastasis by inducing the expression of COX-2 and PGE2 in stromal cells and tumor cells in the hypoxic microenvironment (24).