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Human chorionic gonadotropin （HCG） is a glycoprotein hormone consisting of two noncovalently bonded subunits, alpha and beta [PMID: 68892], and is normally synthesized by placental trophoblasts during pregnancy. β-HCG is a specific marker for trophoblastic tumors of placenta and gestational tumors. Ectopic expression of β-HCG was found in 20-40% of all common epithelial carcinoma, especially for tumors of the stomach, ovary, liver and lung [PMID: 23017787].