PTGS2 and gastric cancer: High expression of migration-related factors, such as cyclooxygenase 2 (COX-2) [5], Vascular endothelial growth factor (VEGF) [6], CXC chemokine ligand (CXCL)-8 [7], chemokine (C-X-C motif) receptor (CXCR)-2, and CXCL-1 [8], are associated with gastric cancer progression.