Mucins are high molecular eight glycoproteins with 80% carbohydrate contents and the remaining 20% is constituted by protein core. Gastric mucin M1 antigens are detected/found in columnar mucus cells of surface gastric epithelium and in goblet cells of the fetal and precancerous colon but not in those of normal colon. Evidence from the literature suggests that they are associated with the peptide core of mucins Resurgence of gastric mucin reactivity during colonic carcinogenesis is suggested to be due to either re-expression of the peptide core of gastric (or fetal colonic) mucins in the adult colon or due to changes in the glycosylation pattern of mucin which expose the hidden M1 antigens.