It is a cocktail of four highly specific monoclonal antibodies that recognize extracellular as well as intracellular domains of the epithelial cellular adhesion molecule (EpCAM). It is a 40-43kDa transmembrane epithelial glycoprotein, identified as epithelial specific antigen (ESA), or EpCAM. EpCAM is expressed on baso-lateral cell surface in most simple epithelia and a vast majority of carcinomas. This epithelial antigen plays an important role as a tumor-cell marker in lymph nodes from patients with esophageal carcinoma otherwise classified as node-negative. Epithelial antigen has also been suggested as a discriminator between basal cell and baso-squamous carcinomas, and squamous cell carcinoma of the skin.