Thyroid function in gestational trophoblastic neoplasia: evidence that the thyrotropic activity of chorionic gonadotropin mediates the thyrotoxicosis of choriocarcinoma.

An investigation was made of thyroid function in 20 patients with gestational trophoblastic neoplasia. Two patients were judged to be overtly thyrotoxic on the basis of the symptoms and physical findings; both patients had widely metastatic choriocarcinoma, markedly increased serum T4 levels (21.4 and 27.7 micrograms/100 ml), and extremely high levels of serum human chorionic gonadotropin (hCG) (3,220 and 6,720 IU/ml) relative to those of normal gestation(< 100 IU/ml). Three other patients had moderately increased serum T4 levels (13 to 17.1 micrograms/100 ml), moderately increased serum hCG levels (110 to 310 IU/ml), and findings on clinical examination which suggested euthyroidism. Using the mouse thyroid bioassay, we found that the biologic characteristics of the thyroid-stimulating factor were those of purified hCG, and that the levels of thyroid-stimulating activity in both serum and urine correlated closely with the levels of hCG. These results provide evidence that the thyroid-stimulating activity intrinsic to the hCG molecule plays the central pathophysiologic role in choriocarcinoma-associated thyrotoxicosis.