Human chorionic gonadotropin antibody (HCG) is a glycoprotein hormone synthesized in syncytiotrophoblastic cells of the placenta and certain trophoblastic tumors. The hormone-specific alpha chains have molecular weights of 13 kDa. HCG is found in moles and choriocarcinoma, chorionic components of germ cell tumors, and syncytiotrophoblast-like cells in seminoma/dysgerminoma and embryonal carcinoma. In diagnostic pathology, HCG is a valuable marker for classifying germ cell tumors and identifying extragonadal germ cell tumors.