TSH-dependent production of T4 and T3 by metastases of a thyroid carcinoma.

A patient with T4 and T3 production by metastases of a follicular thyroid carcinoma leading to TSH suppression is described. During a period of three years, plasma T4, T3 and TSH levels were measured in the substitution-free periods before the successive iodine-131 retention measurements and iodine-131 therapies, when the patient was at least two weeks without thyroid hormones. From the presented data it can be derived that the production of thyroid hormones by metastases was enhanced by endogenous TSH.