Choriocarcinoma with hyperthyroidism: probable identity of the thyrotropin with human chorionic gonadotropin.

A 15-year-old girl developed severe hyperthyroidism secondary to metastatic choriocarcinoma. Her serum contained high levels of human chorionic gonadotropin (HCG) by radioimmunoassay and had a thyroid-stimulating activity different from that of pituitary thyrotropin (TSH) or of long-acting thyroid stimulator (LATS) in the McKenzie mouse bio-assay. Gradient ultracentrifugation localized this thyroid stimulator to a narrow zone midway between markers of transferrin and ovalbumin. On gel filtration it emerged just before albumin as a single peak coinciding with the peak for HCG. Her HCG was identical to an authentic sample of HCG in position to gel filtration columns and on gel electrophoresis. These results suggest that the thyrotropin of choriocarcinoma is HCG.