Giant cell tumor in the thyroid area: a case report in the novel location and review of literature.

Giant cell tumor of soft tissue (GCT-ST) is a rare benign tumor of low malignant potential. It is thought to be the soft tissue counterpart of giant cell tumors of the bone due to its pathological resemblances. GCT-ST is most commonly found in superficial soft tissue of thigh, trunk and upper extremities. The head and neck region is rarely affected. Here for the first time, we describe a case of GCT-ST in the thyroid region. A 70-year-old female patient presented with a painless swelling in her left neck for the previous three weeks. The condition was initially diagnosed as thyroid goiter and left lobectomy was arranged. Intraoperative findings showed an irregular mass invading the strap muscles and trachea. Complete tumor resection was difficult, and part of the tumor was left in the thyroid bed. Histopathology of the resected specimen showed a mixture of mononuclear round to oval cells and multinucleated osteoclast-like giant cells. The giant cells were CD 68 positive. The patient received a revision surgery 3 months after the first operation to achieve complete resection. There was no recurrence in the first 3-month follow-up. However, 6 months after the revision surgery, the tumor recurred on both sides of the neck. The patient suffered from dysphagia and breathlessness. As further surgery and radiation therapy were not considered, denosumab was used as a novel agent After three months of treatment, the patient showed symptom-relief and tumor-regression. The patient continued to have tumor-regression after 1 year of the denosumab treatment. GCT-ST is a benign tumor, although in this case, it was showing features of malignancy. A review of the literature was conducted to identify previous studies on GCT-ST in the head and neck. We present this case for its rare location and novel treatment with denosumab.