5T4 is an antigen expressed in a number of carcinomas. It is an N-glycosylated transmembrane 72 kDa glycoprotein containing seven leucine-rich repeat regions. 5T4 is often referred to as an oncofetal antigen due to its expression in foetal trophoblast (where it was first discovered) or trophoblast glycoprotein (TPBG).

5T4 is found in tumors including the colorectal, ovarian, and gastric. Its expression is used as a prognostic aid in these cases. It has very limited expression in normal tissue but is widespread in malignant tumors throughout their development. Its confined expression appears to give 5T4 the potential to be useful in cancer immunotherapy. 5T4 is also the target of the cancer vaccine TroVax which is used in the treatment of colorectal cancer.