Immunochemical characterization has shown that though intact hCG is abundantly produced by the placenta and germ cell tumors, it is the serum free β-hCG subunit (independent of the common glycoprotein hormone α subunit [GPHα]) that is also a tumor marker in many non-trophoblastic tumors, which include common epithelial cancers. The gene discussed is CGA; the disease is trophoblastic neoplasm.