Recognizes a 40-43kDa transmembrane epithelial glycoprotein, identified as epithelial specific antigen (ESA), or epithelial cellular adhesion molecule (Ep-CAM). Ep-CAM is expressed on baso-lateral cell surface in most simple epithelia and a vast majority of carcinomas. This antibody has been used to distinguish adenocarcinoma from pleural mesothelioma and hepatocellular carcinoma. It is also useful in distinguishing serous carcinomas of the ovary from mesothelioma. 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.