Production eutopique et ectopique des sous-unites α et β des hormones glycoproteiques

Human chorionic gonadotropin (hCG) is a glycoprotein composed of two subunits, α and β, linked together by a covalent bond. Ectopic production of hCG has been described in various histological types of cancer. Actually, these malignant tumors predominantly secrete the free β subunit (hCGβ) and not hCG. Production of free hCGβ is especially found in patients with bladder, pancreas, uterine and lung tumors. In patients with neuroendocrine tumors, serum levels of free hCGβ are higher in gastrointestinal-pancreatic and lung tumors. The significance of ectopic production of hCGβ - epiphenomena or intrinsic biological role - remains unknown. Several reports on the similar structure of hCGβ and certain growth factors suggest that free hCGβ could have an effect on cell proliferation. Increased serum levels of the free α subunit are found mainly in patients with neuroendocrine tumors localized in the gut or lung. Serum levels may also be raised in patients with a pituitary tumor, but such production is often associated with a rise in other pituitary hormones. The free α subunit plays a role in embryon development and would stimulate production of prolactin by decidual cells. The free α subunit may also play a role in tumor growth.