Ultrastructure of two cases of anaplastic giant cell tumor of the human thyroid gland.

Electron microscopy of two cases of anaplastic giant cell tumor of the thyroid revealed that these neoplasms consisted of pleomorphic cells with large, bizarre-shaped nuclei and relatively little cytoplasm rich in rough endoplasmic reticulum. The presence of various intercellular junctions, the resemblance of tumor cells to non-neoplastic epithelial cells of the thyroid follicles and the observation that follicular remnants were identified in the tumor, support the assumption that these tumors derive from the follicular epithelium and can be regarded as carcinomas. Aggregates of cytoplasmic spherical bodies, ultrastructurally similar to virus particles, were detected in some tumor cells. Further investigation is required to determine the nature of these structures and establish their pathogenetic role. In some tumor cells, tubuloreticular arrays were noted within the dilated cisternae of the endoplasmic reticulum; these may represent ultrastructural manifestations of nonspecific injury.