Ultrastructural observations on a follicular carcinoma of the thyroid gland

Electron microscopic studies were performed on a follicular carcinoma removed from a 31-year-old woman. The tumor was poorly differentiated and inoperable but distinctly follicular in pattern. Ultrastructurally, the neoplasm had many of the features of papillary carcinoma, follicular adenoma, and anaplastic carcinoma. Due to the presence of secretory granules it even somewhat resembled medullary carcinoma, but the granules were distinctly larger, and the production of amyloid was definitely excluded.