PTGS2 and gastric cancer: Moreover, the cyclooxygenase-2 (COX-2)-mediated mechanism for gastric cancer progression regulated by nicotine, such as the PKC-ERK1/2-activator protein-1 (AP-1)-COX-2 signaling pathway mediated by activating the β-AR, COX-2/periostin pathway and COX-2/vascular endothelial growth factor (VEGF)/VEGF receptor pathway, has been reported [49].