Human Thyroid Tumors Composed of Mitochondrion-Rich Cells: Electron Microscopic and Biochemical Findings

Abstract

In 9% of a series of 160 thyroid tumors (130 malignant and 30 benign), the only or the predominant cell type was the oxyphilic Hürthle cell. Three carcinomas (follicular or papillary) and two adenomas were evaluated by histochemical, electron microscopic and biochemical techniques. The characteristic cytological features were: cytoplasm loaded with mitochondria of relatively normal structural architectonics, and an increased number of cytoplasmic dense bodies which possessed acid phosphatase and nonspecific esterase activities and therefore could be classified as lysosomes. The mitochondria isolated from Hürthle cell tumors contained higher than normal activity of succinoxidase and cytochrome oxidase and exhibited normal difference spectrum. One follicular carcinoma and one follicular adenoma contained considerable amounts of a poorly iodinated thyroglobulin. When studied, the peroxidase and iodination activities were present but lower than normal. The subcellular distribution of perioxidase and iodination activity was the same as in normal thyroid tissue. It is concluded that Hürthle cell or mitochondrion-rich cell tumors of the thyroid are a variant of follicular thyroid epithelium. Limited data suggest that they contain oxidative enzyme activity which is greater than normal. They may also possess enzymatic activities involved in thyroid hormone synthesis, such as peroxidase-iodination activity, and in certain cases they produce thyroglobulin and hence are potentially able to synthesize thyroid hormones.