OSTEOGENIC ANAPLASTIC CARCINOMA OF THE THYROID

An unusual osteogenic anaplastic carcinoma of the thyroid developed in a 68-year-old man and showed follicular and osteosarcomatous componen ts. Seven months after surgery and 70 MCi I-131 treatment, a local tum or recurrence was found and showed an intense uptake of Tc-99m-MDP on the bone scan. After a second operation, pathologic and immunostaining analysis revealed no more thyroid carcinoma but only osteosarcomatous cells. Chemotherapy was ineffective and the patient died with diffuse pulmonary metastases 26 months after the diagnosis. The importance of osteogenic sarcomatous differentiation is proven by the bone scan. Os teosarcoma of the thyroid is a rare but well known tumor. Usually thes e tumors do not contain any cells originating from the thyroid epithel ium and only comprise sarcomatous components. Ten cases of undifferent iated carcinoma of thyroid origin with osteogenic component have been reported. These tumors have been recently included in undifferentiated carcinomas in the second edition of the WHO classification. The evolu tion and pathologic findings favor the hypothesis of a transdifferenti ation of the thyroid cell into osteogenic cells.