Cyclooxygenase-2 expression in early gastric cancer, intestinal metaplasia and Helicobacter pylori infection.

Cyclooxygenase (COX) is the crucial enzyme for synthesis of prostaglandins and occurs in two isoforms COX-1 and COX-2. Whilst COX-1 is constantly expressed in the gastrointestinal tract in large quantities and probably maintains mucosal integrity through constant generation of prostaglandins, COX-2 is induced principally during inflammation. In early gastric cancer and in intestinal metaplasia the expression of COX-2 in patients infected by Helicobacter pylori is increased in intestinal type compared to diffuse type gastric cancer and in intestinal metaplasia. In tumours of mixed type, COX-2 is also increased in the intestinal component compared to the diffuse component. Whilst there has been success of COX-2 inhibition for chemoprevention in colon cancer, a similar role in gastric cancer needs to be carefully assessed in the light of reported adverse effects and whether the precancerous condition, intestinal metaplasia, can truly regress.