Mucin 5AC glycoprotein (MUC5AC) is a 641 kDa glycoprotein belonging to the superfamily of mucins. Mucins are high molecular weight glycoproteins produced by epithelial cells and can be divided into two families; secretory mucins and membrane bound mucins. MUC5AC is a mucus-forming secreted mucin that is found in normal gastric and tracheo-bronchial mucosa, but absent from normal colon. MUC5AC expression is present in primary ovarian mucinous cancer but usually absent in colorectal adenocarcinoma, thus showing an expression pattern opposite to MUC2.
Anti-MUC5AC is a useful aid for classification of primary mucinous ovarian tumors. MUC5AC antibodies are also a useful aid for classification of intestinal metaplasia as well as in the classification of pancreatic carcinoma.