Effect of Thyroidectomy with and Without Thyroxine Replacement on Transplantable Thyroid Tumors in Rats

Abstract

Transplanted autonomous thyroid tumors grew to a larger size in rats receiving replacement thyroxine after radioiodine thyroidectomy than in rats permitted to continue in a myxedematous state. This effect of thyroxine on neoplasm growth may not be directly on the tumor, in that no significant deiodination of thyroxine by the tumors was demonstrated. Tumor uptake of ¹³¹I per unit weight was greater in the neoplasms from the hypothyroid animals. (Endocrinology74: 925, 1964)