5T4 is an antigen expressed in a number of carcinomas (oncofetal antigen or oncofetal trophoblast glycoprotein). It is a N-glycosylated transmembrane 72 kDa leucine-rich repeat glycoprotein.

5T4 is found in tumours 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 tumours throughout their development.

Its confined expression appears to give 5T4 the potential to be useful in cancer immunotherapy. There has been extensive research into its role in antibody-directed immunotherapy through the use of the high-affinity murine monoclonal antibody, mAb5T4, to deliver response modifiers (such as staphylococcus aureus superantigen) accurately to a tumour.