TACD2 is a transmembrane glycoprotein originally identified in trophoblasts. It functions to maintain epithelial barrier function and localization of tight junctional proteins. It acts as a cell surface receptor that transduces intracellular calcium, but its endogenous ligand has not been identified. Expression is broadly observed in many normal tissues and is frequently overexpressed in a variety of tumors including papillary thyroid carcinoma (PTC).