Effect of TSH stimulation on serum thyroglobulin in metastatic thyroid cancer.

Thyroglobulin (TG) is a glycoprotein which has been found to be produced by almost all nonmedullary thyroid cancers, and is present in elevated levels in the serum of most patients with metastatic thyroid cancer. It has long been a clinical impression that many metastatic thyroid cancers are "responsive" to TSH suppression as manifested by a decrease in the size and/or symptoms of the tumor. Five athyroid patients with metastatic thyroid cancer were studied to determine the effect of TSH stimulation on their serum TG levels and attempt to correlate this effect with their clinical response. Three of the five patients showed a definite rise in their serum TG once serum thyroxine (T4Y replacement was withdrawn, which correlated with an increase in TSH, and two of these patients have had no progression of their disease while on T4 suppression. The remaining two patients have shown no change in their TG levels after T4 withdrawal, and both have had progression of their metastatic disease while on T4 suppression. Thus, we see that in some patients, TG production by their metastatic thyroid cancer is responsive to TSH suppression, and there is some suggestion that TSH-responsive cancers are less aggressive; but it will require further studies to determine this.