PTGS1 and gastric cancer: COX-1 is a structural enzyme that is expressed in most normal tissues, and COX-1 promotes prostaglandin production, thereby maintaining normal human function (13); COX-2 is an inducible enzyme that is rarely expressed in normal tissues, but often highly expressed in tumor cells, such as melanoma, colon cancer, breast cancer, liver cancer, cervical cancer, esophageal cancer, pancreatic cancer, and gastric cancer (14).