[Multinucleated giant cell tumor of the thyroid: an unusual anaplastic carcinoma (author's transl)].

Neoplasms of the thyroid with multinucleated, osteoclast-like giant cells, are rare. The numerous giant cells observed in these undifferentiated neoplasm have extensive eosinophilic cytoplasm and contain two to several hundred round or oval, uniform small nuclei. The clinical and morphologic data obtained from the two cases we describe and seven others collected from the literature are as follows: a) peak incidence in late adulthood; b) frequent association with a preexisting goiter (6 cases); c) rapid growth and fatal outcome within one year following diagnosis (5 cases); d) histologic pleomorphism with a background of uniform and spindle- or bizarre-shaped mononuclear cells; e) occasional coexistence of multinucleated giant cell tumor with well differentiated follicular carcinoma (1 case). Indirect evidence suggests that the multinucleated giant cells which characterize these unusual anaplastic carcinomas are epithelial in origin.