Human Chorionic Gonadotropin (HCG) is a glycoprotein, which is secreted in large quantities by normal trophoblasts.
It is present only in trace amounts in non-pregnant urine and sera but rises sharply during pregnancy.
HCG is composed of two non-identical, non-covalently linked polypeptide chains designated as the a-and b-subunits.
The a-subunit of HCG is nearly identical to that of thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH), and luteinizing hormone (LH).
A germ cell tumor which is positive for cytokeratin, placental alkaline phosphatase (PLAP), and HCG but negative for EMA and AFP is probably a choriocarcinoma.
Staining of formalin/paraffin tissues is enhanced by boiling tissue sections in 10mM citrate buffer, pH 6.0, for 10-20 min., followed by cooling at RT for 20 min.