MUC1 (EMA) is a membrane-bound protein, a large, heavily glycosylated mucin expressed on the apical surfaces of most simple, secretory epithelia including the mammary gland, gastrointestinal, respiratory, urinary and reproductive tracts. This protein is proteolytically cleaved into alpha and beta subunits that form a heterodimeric complex. The N-terminal alpha subunit functions in cell-adhesion and the C-terminal beta subunit is involved in cell signaling.. Overexpression, aberrant intracellular localization, and changes in glycosylation of this protein have been associated with carcinomas. MUC1 E29 stains normal and neoplastic cells from various tissues, including mammary and respiratory epithelium. The MUC1 is aberrantly overexpressed by most human carcinomas. It associates with the p53 tumor suppressor, and this interaction is increased by genotoxic stress. MUC1 cytoplasmic domain binds directly to p53 regulatory domain.