Fine structure of human papillary thyroid carcinoma

The fine structure of 5 human papillary thyroid carcinomas was described and compared with previous publications on the ultrastructure of the normal gland and of diffuse hyperplastic goiter. The 5 tumors were composed of predominantly tall columnar epithelial cells. Interspersed with the neoplastic cells and inside the epithelial basement membrane were a few lymphocytes, the significance of which is undetermined. Most neoplastic cells showed numerous mitochondria and cytosomes. A well-developed granular endoplasmic reticulum and a prominent Golgi apparatus often were observed. Microvilli, cytoplasmic protrusions, apical vesicles, multivesicular bodies, microfibrils, and microtubules also were identified. Nuclei were large, were often indented, and contained prominent nucleoli and distinct granulofibrillar inclusions in two different stages of development. Their etiology is unknown. Nuclear structures containing cytoplasmic organelles were common and were caused by invagination of the nuclear envelope. Except for the intranuclear inclusions, more variation in the size and shape of the nuclei, and absence of colloid droplets, human papillary thyroid carcinoma cells closely resemble hyper-plastic follicular cells.