Solitary Fibrous Tumor Arising in an Intrathoracic Goiter

Background: Solitary fibrous tumor (SFT) is a rare spindle cell tumor most often found in the mediastinal pleura. Nineteen cases of SFT arising in the thyroid gland have been reported. We report a case of SFT of the thyroid gland with immunohistochemical and cytogenetic investigation. Summary: A 58-year-old man had pulmonary symptoms, thought to be asthma. Computed tomographic scan revealed a large goiter with a solid hyperechoic nodule. The results of thyroid function tests were normal. Microscopically, the lesion was composed of fibroblast-like spindle cells in a patternless growth. Cellular atypia or necrosis was not seen, and mitotic activity was low. Immunohistochemistry showed positive reaction for CD34, vimentin, bcl-2, and CD99. Fluorescence in situ hybridization analysis of more than 100 cells exhibited no trisomy 21. Complete surgical removal of tumor is the treatment of choice. Conclusion: The histological appearance and immunohistochemical reaction pattern of SFT is characteristic. The entity should be considered when dealing with a spindle cell lesion in the thyroid gland. All cases of this site of origin reported have had a benign clinical course. As only a small number of cases have been described, we recommend long-term follow-up.