Isolated ectopic production of the free beta subunit of chorionic gonadotropin by an epidermoid carcinoma of unknown primary site

Abstract

Metastatic choriocarcinoma was suspected in a 39-year-old woman who presented 7 months postpartum with fatigue, pelvic pain, a massive pleural effusion, and a positive urine pregnancy test. Subsequent evaluation resulted in discovery of the isolated production of the freeβ-subunit of chorionic gonadotropin (CG-β) by a widespread, poorly differentiated epidermoid carcinoma. Chemotherapy was ineffective, the woman died, and at autopsy the primary site of the tumor could not be determined. The patient's serum (185 ng/ml) and a tumor metastasis (720 ng/g) contained large amounts of immunoactive material that diluted in parallel to CG-β standard, but neither chorionic gonadotropin (CG), its alpha subunit, nor other placental proteins were detected. A monoclonal antibody that recognizes free CG-β, but not intact CG, was instrumental in implicating an ectopic source of the CG-β before a tissue diagnosis was obtained. When the patient's serum was chromatographed on a dextran gel, the CG-β immunoactivity eluted in a position of higher apparent molecular weight than either standard CG or CG-β, suggesting that this neoplasm secreted an altered molecular form of the CG-β subunit.