The fine structure of human thyroid cancer.

This ultrastructural description of human thyroid cancers is based on the available literature and on our own studies of about 150 cases. Electron microscopy is an invaluable diagnostic adjunct to light microscopy, as it may eliminate inaccurate designations such as "small cell malignant tumors of the thyroid," which include tumors of different histogenetic origin with a different prognosis and treatment that share only a similarity in appearance under the light microscope. Ultrastructure is also of diagnostic importance in cases of medullary carcinoma that imitate papillary or follicular patterns or lack amyloid stroma. Its importance in separating follicular adenomas from carcinomas, however, has not been proven. In conjunction with other methods ultrastructural study might throw new light on the controversial classification of papillary and follicular carcinomas and improve our understanding of their different biologic behavior. Immunoelectron microscopy may help in solving the problem of amyloid pathogenesis in endocrine tumors and in charting the subcellular mechanisms involved in the production of multiple polypeptide hormones in a single tumor.