The Derivation of So-called “Giant-cell” and “Spindle-cell” Undifferentiated Thyroidal Neoplasms

Abstract

Electron microscopy of a combined giant-cell and spindle-cell undifferentiated neoplasm of the thyroid disclosed the presence of frequent desmosomal attachment plates, occasional microvilli, and apparent transitional forms between remaining acinar and overtly neoplastic cellular elements. The conversion of round and giant cells to more spindle forms could be followed in tissue culture explants of the primary tumor, indicating that all cell types in this tumor represent morphologic variants of die same prototype element. The ultrastructural features of these cells in tissue culture were similar to those noted in the cells of die primary tumor. These findings signify the epithelial derivation of this common form of undifferentiated thyroid neoplasm. On the other hand, the ultrastructural features of cells comprising another undifferentiated, purely spindle-cell, thyroidal neoplasm allowed for their identification as fibroblasts and its designation as fibrosarcoma. The presence of both giant and round cells, occasional epidielial-like architectural arrangement of cell masses, and apparent transitions of the neoplastic elements from occult acini should allow for die light microscopic differentiation of this carcinoma with spindle cells from the uniformly spindle-cell, truly sarcomatous-appearing fibrosarcoma.