Solitary fibrous tumor (SFT) is a spindle-cell neoplasm that rarely arises from the thyroid gland. The first ever case of thyroid SFT was reported in 1993. Since then, 42 cases have been reported in the literature. The tumor showed benign clinical characteristics in all of the cases, except one, where the patient presented with a local recurrence and distant metastasis.
We report two cases of thyroid SFT. In the first, a 70-year-old man presented with a 4-year history of a gradually growing thyroid tumor. We performed left hemithyroidectomy. Histologically, the tumor consisted of infiltrating spindle cells with no mitoses. The patient was doing well after 2 months. In the second case, a 44-year-old man presented with a 10-year history of an enlarging neck mass and CT showed the mass excluding the trachea in the left thyroid lobe. Fine needle aspiration cytology performed under ultrasound guidance demonstrated a hypocellular aspirate that revealed spindle cells. We performed left hemithyroidectomy. Histologically, the mass had a clearly defined fibrous capsule. The tumor was hypercellular, composed of epithelioid neoplastic cells with cytologic atypia. The mitotic count was markedly elevated to 10/10 high-power fields. After 5 months, PET-CT showed distant metastasis. Postoperative chemotherapy was unsuccessful, and the patient died 29 months after the operation.
The clinical course in patients with SFT is often not consistent with the histologic features. Therefore, recently, Demicco et al. established a risk stratification model based on the age, tumor size, mitotic figure count, and necrosis. We attempted to validate this model for thyroid SFT by applying it to our cases and to the retrospective case series, and were able to identify the case with local recurrence and distant metastasis using this model. Therefore, surgical management to obtain adequate negative margins and long-term follow-up can be recommended by patient selection using the risk stratification model.
