THYROID FUNCTION IN CHORIOCARCINOMA: DEMONSTRATION OF A THYROID STIMULATING ACTIVITY IN SERUM USING FRTL‐5 and HUMAN THYROID CELLS

Hyperthyroidism is a well recognized complication of gestational trophoblastic tumours (GTT) and may be due to high circulating concentrations of human chorionic gonadotrophin (hCG) or its variants. We have studied 24 clinically euthyroid women with GTT. Eight were biochemically hyperthyroid with low or undetectable serum thyrotrophin (TSH) and had a mean serum hCG of 3612 |MX 103 IU/1 compared to 76.2 |MX 103 IU/1 in the other patients (P < 0.01). Purified hCG stimulated iodide uptake into FRTL‐5 cells with 25 |MX 103 IU/1 being equivalent in potency to 1 mU/1 of thyrotrophin (TSH). Sixteen out of the 24 sera (67%) stimulated iodide uptake when applied to the cells at a 1:10 dilution. Sera from all eight hyperthyroid patients contained thyroid stimulating activity. The mean hCG concentration in the 16 stimulatory sera was 238.2 |MX 103 IU/1 compared to 37.1 |MX 103 IU/1 in the other eight sera (P < 0.01). Six men with hCG‐secreting testicular tumours were biochemically euthyroid although three of their sera stimulated iodide uptake into FRTL‐5 cells. In human thyroid cells the mean cAMP production over 4 h with sera from five healthy controls was 54.2 |Mp 1.81 pmol/mg cell protein compared to 67.0 |Mp 3.8 pmol/mg protein with sera from five choriocarcinoma patients (P < 0.02). Serum from patients with gestational trophoblastic tumours contains a thyroid stimulating activity which may be hCG and whose presence correlates with hyperthyroidism.