Giant cell tumor of soft tissue involving thyroid gland: a case report and review of the literature

Background: Giant cell tumor of soft tissue is a low malignant uncommon neoplasm, with histologic features and immunophenotype similar to its bone counterpart. Primary giant cell tumor of soft tissue in the thyroid gland is considered an exceedingly rare entity. Case presentation: We describe a case of primary thyroid giant cell tumor of soft tissue in a 69-year-old Chinese female patient. Neck ultrasonography showed a 19 mm × 12 mm × 5 mm nodule with heterogeneous echo and clear boundary located within the left thyroid. Histopathological examination revealed that the neoplasm was composed of two morphological components, mononuclear cells admixed with multinucleated osteoclast-like giant cells. Immunohistochemically, the tumor cells were positive for CD68 and vimentin, but were negative for epithelial membrane antigen, cytokeratin, and additional muscle markers. She underwent left unilateral thyroidectomy, and total thyroidectomy was performed for local recurrence 3 months later. The patient remained well without recurrence or metastasis following up for 12 months. Conclusion: The significance of this case lies in its rarity, the challenge of preoperative clinical diagnosis, and the differential diagnosis with other malignancies.