This MAb recognizes the peptide core of gastric mucin M1 (recently identified as Mucin 5AC). Its epitope is located in the N-terminal cysteine rich part of the peptide core of MUC5AC, which is heavily glycosylated. Its epitope is destroyed by beta-mercaptoethanol but not by periodate treatment. MAb 2-11M1 reacts with the protein backbone exclusively; it only reacts with fully deglycosylated MUC5AC. Therefore, the material under test should also be fully deglycosylated. This can be achieved with standard periodate oxidation method. The success of the deglycosylation can be checked with routine PAS (Periodic Acid Shiff) staining. After deglycosylation, the preparation should no longer be stainable with PAS reagent. Only then 2-11M1 will react should MUC5AC be present. This mucin is present in primary ovarian mucinous cancer but usually absent in colorectal adenocarcinoma, thus showing an expression pattern opposite to MUC2. Together with a panel of antibodies, Anti-MUC5AC may be useful for differential identification of primary mucinous ovarian tumors from colon adenocarcinoma metastatic to the ovary. MUC5AC antibodies may also be useful for identification of intestinal metaplasia as well as in the identification of pancreatic carcinoma and pre-cancerous changes vs. normal pancreas.