Electron microscopic investigations about the differentiation of thyroid carcinoma

36 thyroid carcinomas have been studied by means of electron microscopy. The specimens of 12 non-malignant thyroid lesions served as control. All the investigated tumours are composed of mixed populations of tumour cells differentiated in manifold variations. Differentiated carcinomas (follicular, papillary) often show misdifferentiations of the cytoplasm in light microscope, as well as in electron microscope. These misdifferentiations are the hyperplasia of a single cytoplasmatic organella or the hyperplasia of a system of organellas. The hyperplasia can be combined with a normal appearance of the respective organellas or with pathological changes of their morphology. Undifferentiated tumours often show structural remnants of folliculoid differentiation.