Mucins are a diverse collection of complex proteins that are highly glycosylated and located outside of cells. Mucin 2 (MUC2) acts to protect the epithelial surfaces of the stomach and intestines against both chemical and physical harm. Responses against MUC2 are commonly found in the goblet cells of the small intestine and colon, and these responses are associated with mucinous tumors, including those in the gastrointestinal tract and ovaries. The use of MUC2 immunohistochemistry is helpful in identifying cancers present in the colon, stomach, and esophagus.