5T4 (oncofetal antigen 5T4; also TPBG and trophoblast glycoprotein) is a member of the LRR family of proteins. It is expressed on trophoblasts, tumor cells, ovarian cuboidal epithelium and embryonic stem cells, and impacts cell adhesion and motility.

Human 5T4 is a 72kD glycoprotein. The human 5T4 cDNA encodes a type I transmembrane protein precursor that is 420 amino acids (aa) in length. It contains a 324 aa extracellular region (aa 32 - 355) that shows one Ser-rich region followed by seven Leu-rich repeats (aa 90 - 355). Over aa 31 - 355, human 5T4 shares 81% and 85% aa identity with mouse and canine 5T4, respectively.