Solitary fibrous tumor arising in an intrathoracic goiter

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.

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.

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.