PTGS2 and neoplasm: In tumor hypoxic microenvironment, tumor cells, tumor associated macrophages, dendritic cells, myeloid derived suppressor cells, and neutrophil cells secrete a variety of proangiogenesis and prolymphangiogenesis factors (e.g., VEGF, VEGF-C, MMP-9, TGF-β, and COX-2) [18, 19].