Abstract: Background and purpose: Primary solitary fibrous tumor (SFT) of thyroid is very rare. This study aimed to explore the clinicopathological features and identification of thyroid SFT. Methods: We analyzed one case of primary thyroid SFT treated in Affiliated Hospital of Xuzhou Medical University, including the clinical manifestations, histological features and immunohistochemical phenotypes, and reviewed the relevant English literature. Results: The patient was a 37-year-old male with a well-circumscribed mass in the right lobe of the thyroid gland, and the mass was 3.2 cm in diameter. Microscopically, the tumor displayed proliferation of spindle cells growing in nonspecific “patternless” manner with few amounts of intercellular collagen bundles. The tumor vessels showed branching staghorn-like appearance. Immunohistochemistry showed the spindle cells were positive for signal transducers and activators of transcription 6 (STAT6) (strong, nuclear), vimentin, CD34, CD99 and Bcl-2 (weak). The patient was followed up for 15 months and in good condition. A total of 25 cases reported in the English literature were followed up for 5-160 months. Only one malignant case had reccurrence and metastasis after 5 months. Conclusion: Thyroid SFT is an uncommon neoplasm, and histopathology and immunohistochemistry can confirm the diagnosis. Most of the tumors are benign with good prognosis. Malignant cases are rare with the risk of recurrence and metastasis. Long-term follow-up is essential to evaluate the prognosis, and surgical resection is the preferred treatment for SFT.

Key words: Solitary fibrous tumor, Thyroid, Immunohistochemistry, Signal transducers and activators of transcription 6