Trophoblast glycoprotein (TPBG), also known as 5T4, is a therapeutic target for several anticancer agents in clinical development. This is primarily due to its high expression in tumors and low expression in normal adult tissues. The TPBG gene encodes a leucine-rich transmembrane glycoprotein that may play a role in cell adhesion. TPBG is expressed by all types of trophoblasts as early as the ninth week of development.